Stacked body for flexible display device, stacked body for display device and flexible display device

ABSTRACT

The present disclosure provides a stacked body for a flexible display device comprising a substrate layer, and an antistatic layer, wherein a contact angle with respect to water, of an antistatic layer side surface of the stacked body for a flexible display device, is 100° or more; a ratio of a contact angle with respect to water after a steel wool test, with respect to an initial contact angle with respect to water, of the antistatic layer side surface of the stacked body for a flexible display device is, 0.6 or more, wherein, in the steel wool test, the antistatic layer side surface of the stacked body for a flexible display device is rubbed with a #0000 steel wool, for 2500 strokes, applying a load of 9.8 N; a surface resistance of the antistatic layer side surface of the stacked body for a flexible display device is 9×1013Ω/□ or less; and a surface resistance of the antistatic layer side surface of the stacked body for a flexible display device after an eraser test is 9×1013Ω/□ or less, wherein, in the eraser test, the antistatic layer side surface of the stacked body for a flexible display device is rubbed with a 6 mm diameter eraser, for 2500 strokes, applying a load of 9.8 N.

TECHNICAL FIELD

The present disclosure relates to a stacked body for a flexible displaydevice, a stacked body for a display device, and a flexible displaydevice.

BACKGROUND ART

For example, a stacked body provided with a functional layer havingvarious properties such as a hard coating property, a scratchresistance, antireflection property, an antiglare property, anantistatic property, and an antifouling property, is placed on thesurface of a display device.

As a substrate layer for such a stacked body, for example, a glasssubstrate and a resin substrate are used. However, the glass substrateand resin substrate are highly insulating, so they are easilyelectrified, and become dirty due to adhesion of dust and dirt, forexample. Also, when static electricity is generated in the productionprocess of a display device, so-called electrostatic breakdown mayoccur, in which the electronic components constituting the displaydevice are damaged by the charged static electricity being discharged.Also, there is a possibility that display device is electrified when adevice such as a battery is installed to the display device. Therefore,it is conventionally known to use a stacked body including an antistaticlayer in order to prevent such electrification.

In recent years, not only smart phones and tablet terminals but alsodisplay devices such as notebook type personal computers have a touchfunction. In a display device having a touch function, abrasionresistance and sliding property are required since they are operated bydirectly touching the surface thereof with a finger or the like.

Also, portable display devices such as smart phones and tablet terminalsmay be stored in, for example, pockets of clothing or a bag so that thesurface of the display devices may be rubbed with the cloth of theclothing or a bag, or with other items stored in the pockets of clothingor a bag. For this reason, further abrasion resistance is required forthe portable display devices.

CITATION LIST Patent Documents

-   -   Patent Document 1: Japanese Patent Application Laid-Open (JP-A)        No. 2016-125063    -   Patent Document 2: Japanese Patent No. 6140348

SUMMARY OF DISCLOSURE Technical Problem

In recent years, flexible displays such as a foldable display, arollable display, and a bendable display have been attracting attention,and a stacked body placed on the surface of the flexible display hasbeen actively developed. For example, a use of a resin substrate insteadof a glass substrate has been studied, and for example, Patent Document1 proposes a display device window film comprising a plastic substratehaving high hardness and excellent optical properties, and a hardcoating layer placed on at least one surface of the plastic substrate.

Since flexible displays are used or stored in a bent condition, forexample, the surface of the bent portion is likely to be rubbed.Therefore, in the flexible display, further superior abrasion resistanceis required in the bent portion.

Generally, examples of a known approach to increase the abrasionresistance may include an increase of the surface hardness, and adecrease of the friction coefficient.

However, in a case where the surface hardness is increased, in a stackedbody used for a flexible display, when the surface hardness isincreased, flexibility such as folding property (foldable), windingproperty (rollable), and bending property (bendable) may be impaired.

Also, as a method for reducing the friction coefficient, for example, atechnique of imparting low friction property by applying a fluorinebased surface treatment agent or by adding a fluorine based additive isknown. For example, Patent Document 2 discloses a surface treatmentagent including a fluorooxyalkylene group-containing polymer compositioncapable of providing a coating excellent in water repellency-oilrepellency, scratch resistance, low dynamic friction, and abrasionresistance.

However, since the surface of the functional layer is rubbed, thecomponent included in the functional layer in the stacked body may berubbed away, or the functional layer may be worn down, so that theperformance of the functional layer may be deteriorated. Therefore, asdescribed above, further improvement in abrasion resistance is desiredin the flexible display.

The present disclosure has been made in view of the above circumstances,and a main object of the present disclosure is to provide a stacked bodyfor a flexible display device and a flexible display device excellent inabrasion resistance.

Solution to Problem

In order to solve the problems, the inventors of the present disclosurehave focused on a steel wool test and an eraser test as an abrasiontest, and as the result of intensive studies on the abrasion resistanceof the stacked body for a flexible display device, they have found outthat the eraser resistance may be inferior in some cases, even when thesteel wool resistance is excellent. Further, the inventors of thepresent disclosure have intensively studied, and they have surprisinglyand newly found out that the abrasion resistance and the surfaceresistance are correlated with each other. The present disclosure isbased on such findings.

One embodiment of the present disclosure provides a stacked body for aflexible display device comprising a substrate layer, and an antistaticlayer, wherein a contact angle with respect to water, of an antistaticlayer side surface of the stacked body for a flexible display device, is100° or more; a ratio of a contact angle with respect to water after asteel wool test, with respect to an initial contact angle with respectto water, of the antistatic layer side surface of the stacked body for aflexible display device, is 0.6 or more, wherein, in the steel wooltest, the antistatic layer side surface of the stacked body for aflexible display device is rubbed with a #0000 steel wool, for 2500strokes, applying a load of 9.8 N; a surface resistance of theantistatic layer side surface of the stacked body for a flexible displaydevice is 9×10¹³Ω/□ or less; and a surface resistance of the antistaticlayer side surface of the stacked body for a flexible display deviceafter an eraser test is 9×10¹³Ω/□ or less, wherein, in the eraser test,the antistatic layer side surface of the stacked body for a flexibledisplay device is rubbed with a 6 mm diameter eraser, for 2500 strokes,applying a load of 9.8 N.

In the stacked body for a flexible display device in the presentdisclosure, a ratio of the surface resistance of the antistatic layerside surface of the stacked body for a flexible display device after theeraser test, with respect to an initial surface resistance, ispreferably 20.0 or less.

Also, in the stacked body for a flexible display device in the presentdisclosure, the antistatic layer preferably includes an antifoulant.

Also, in the stacked body for a flexible display device in the presentdisclosure, an impact absorbing layer may be included on the substratelayer, on an opposite surface side to the antistatic layer, or betweenthe substrate layer and the antistatic layer.

Also, in the stacked body for a flexible display device in the presentdisclosure, a pressure-sensitive adhesive layer for adhesion may beincluded on the substrate layer, on an opposite surface side to theantistatic layer.

Another embodiment of the present disclosure provides a stacked body fora display device comprising a substrate layer, and an antistatic layer,wherein a contact angle with respect to water of, an antistatic layerside surface of the stacked body for a display device, is 100° or more;a ratio of a contact angle with respect to water after a steel wooltest, with respect to an initial contact angle with respect to water, ofthe antistatic layer side surface of the stacked body for a displaydevice, is 0.6 or more, wherein, in the steel wool test, the antistaticlayer side surface of the stacked body for a display device is rubbedwith a #0000 steel wool, for 2500 strokes, applying a load of 9.8 N; asurface resistance of the antistatic layer side surface of the stackedbody for a display device is 9×10¹³Ω/□ or less; and a surface resistanceof the antistatic layer side surface of the stacked body for a displaydevice after an eraser test is 9×10¹³Ω/□ or less, wherein, in the erasertest, the antistatic layer side surface of the stacked body for adisplay device is rubbed with a 6 mm diameter eraser, for 2500 strokes,applying a load of 9.8 N.

Another embodiment of the present disclosure provides a flexible displaydevice comprising: a display panel, and the stacked body for a flexibledisplay device described above placed on an observer side of the displaypanel.

Advantageous Effects of Disclosure

The present disclosure has an effect that a stacked body for a flexibledisplay device, a stacked body for a display device, and a flexibledisplay device excellent in abrasion resistance may be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating an example of astacked body for a flexible display device in the present disclosure.

FIG. 2 is a schematic view explaining a method for measuring a frictionforce with respect to an eraser.

FIGS. 3A to 3C are schematic views explaining a dynamic bending test.

FIG. 4 is a schematic cross-sectional view illustrating an example of astacked body for a flexible display device in the present disclosure.

FIG. 5 is a schematic cross-sectional view illustrating an example of astacked body for a flexible display device in the present disclosure.

FIG. 6 is a schematic cross-sectional view illustrating an example of aflexible display device in the present disclosure.

DESCRIPTION OF EMBODIMENTS

Embodiments in the present disclosure are hereinafter explained withreference to, for example, drawings. However, the present disclosure isenforceable in a variety of different forms, and thus should not betaken as is limited to the contents described in the embodimentsexemplified as below. Also, the drawings may show the features of thepresent disclosure such as width, thickness, and shape of each partschematically comparing to the actual form in order to explain thepresent disclosure more clearly in some cases; however, it is merely anexample, and thus does not limit the interpretation of the presentdisclosure. Also, in the present description and each drawing, for thefactor same as that described in the figure already explained, the samereference sign is indicated and the detailed explanation thereof may beomitted.

In the present descriptions, in expressing an aspect wherein some memberis placed on the other member, when described as merely “on” or “below”,unless otherwise stated, it includes both of the following cases: a casewherein some member is placed directly on or directly below the othermember so as to be in contact with the other member, and a case whereinsome member is placed on the upper side or the lower side of the othermember via yet another member. Also, in the present descriptions, on theoccasion of expressing an aspect wherein some member is placed on thesurface of the other member, when described as merely “on the surfaceside” or “on the surface”, unless otherwise stated, it includes both ofthe following cases: a case wherein some member is placed directly on ordirectly below the other member so as to be in contact with the othermember, and a case wherein some member is placed on the upper side orthe lower side of the other member via yet another member.

The inventors of the present disclosure have focused on a steel wooltest and an eraser test as an abrasion test, and as the result ofintensive studies on the abrasion resistance of the stacked body for aflexible display device, they have found out the following knowledges.

Firstly, they have focused on the contact angle with respect to water,of the surface of the stacked body for a flexible display device. Whenthe variation ratio of the contact angle with respect to water after asteel wool test, with respect to the initial contact angle with respectto water is low, it can be said that the performance may be maintainedeven after the steel wool test, so that it can be said that the abrasionresistance is high.

However, as the result of studies, the inventors of the presentdisclosure have found out that the variation ratio of the contact anglewith respect to water after the eraser test, with respect to the initialcontact angle with respect to water may be high in some cases, even whenthe variation ratio of the contact angle with respect to water after thesteel wool test, with respect to the initial contact angle with respectto water is low. That is, they have found out that the eraser resistancemay be inferior in some cases, even when the steel wool resistance isexcellent.

Therefore, the inventors of the present disclosure have studied aboutthe variation of friction force before and after the eraser test bycarrying out an eraser test to the stacked body for a flexible displaydevice. By focusing on the eraser test and the surface resistance, andmeasuring the friction force and the surface resistance before and afterthe eraser test, they have found out that, although both of the frictionforce and the surface resistance tend to increase after the eraser test,the variation of the friction force before and after the eraser testtends to be relatively low, when the surface resistance after the erasertest is relatively low; and when the surface resistance after the erasertest is relatively high, the variation of the friction force before andafter the eraser test tends to be relatively high. Further, they havefound out that, when the initial surface resistance before the erasertest is low, the surface resistance after the eraser test tends to below. That is, they have found out that the abrasion resistance and thesurface resistance after the eraser test are correlated with each other.Further, they have found out that the abrasion resistance may be easilyinferred from the initial surface resistance before the eraser test. Inother words, they have newly found out that the abrasion resistance andthe surface resistance before and after the eraser test are wellcorrelated with each other. Further, by studying the correlation betweenthe abrasion resistance and the surface resistance before and after theeraser test in detail, they have found out that, in order to impartexcellent abrasion resistance, it is importance to make the surfaceresistance before and after the eraser test to be a predetermined valueor less.

In the present disclosure, it is very meaningful to find out thedecrease of the surface resistance after an eraser test as an index ofimproving the abrasion resistance. Further, it is very meaningful tofind out the initial surface resistance before an eraser test as anindex to infer the abrasion resistance.

Here, the reason for using a steel wool in the abrasion test is becausea steel wool test is generally applied to evaluate the abrasionresistance. By the steel wool test, for example, the abrasion resistancewith respect to relatively hard matter such as an item stored in thepockets of clothing or a bag may be evaluated.

Also, the reason for using an eraser in the abrasion test is becauserubbing with an eraser is similar to rubbing with a stylus pen, and bythe eraser test, for example, the abrasion resistance with respect torelatively soft matter such as a stylus pen, a finger, cloth of clothingor a bag may be evaluated.

A stacked body for a flexible display device, a stacked body for adisplay device, and a flexible display device in the present disclosureare hereinafter described in detail.

A. Stacked Body for a Flexible Display Device

The stacked body for a flexible display device in the present disclosurecomprises a substrate layer, and an antistatic layer, wherein a contactangle with respect to water, of an antistatic layer side surface of thestacked body for a flexible display device, is 100° or more; a ratio ofa contact angle with respect to water after a steel wool test, withrespect to an initial contact angle with respect to water, of theantistatic layer side surface of the stacked body for a flexible displaydevice, is 0.6 or more, wherein, in the steel wool test, the antistaticlayer side surface of the stacked body for a flexible display device isrubbed with a #0000 steel wool, for 2500 strokes, applying a load of 9.8N; a surface resistance of the antistatic layer side surface of thestacked body for a flexible display device is 9×10¹³Ω/□ or less; and asurface resistance of the antistatic layer side surface of the stackedbody for a flexible display device after an eraser test is 9×10¹³Ω/□ orless, wherein, in the eraser test, the antistatic layer side surface ofthe stacked body for a flexible display device is rubbed with a 6 mmdiameter eraser, for 2500 strokes, applying a load of 9.8 N.

FIG. 1 is a schematic cross-sectional view illustrating an example of astacked body for a flexible display device in the present disclosure. Asshown in FIG. 1 , stacked body for a flexible display device 1 comprisessubstrate layer 2, and antistatic layer 3. The contact angle withrespect to water of the antistatic layer 3 side surface of the stackedbody for a flexible display device 1 is a predetermined value or more;the ratio of a contact angle with respect to water after a predeterminedsteel wool test, with respect to an initial contact angle with respectto water, of the antistatic layer 3 side surface of the stacked body fora flexible display device 1 is a predetermined value or more. Also, thesurface resistance of the antistatic layer 3 side surface of the stackedbody for a flexible display device 1 is a predetermined value or less.Further, the surface resistance of the antistatic layer 3 side surfaceof the stacked body for a flexible display device 1 after apredetermined eraser test is also a predetermined value or less.

As described above, the present disclosure was achieved based on the newfinding that, in the stacked body for a flexible display device, theabrasion resistance and the surface resistance before and after theeraser test are correlated with each other. In the present disclosure,excellent abrasion resistance may be obtained by the initial contactangle with respect to water of the antistatic layer side surface of thestacked body for a flexible display device being a predetermined valueor more; the ratio of a contact angle with respect to water after asteel wool test, with respect to an initial contact angle with respectto water being a predetermined value or more; and further, the surfaceresistance both before and after an eraser test being a predeterminedvalue or less.

The reason therefor is not clear, but presumed as follows. That is, whenan eraser test is carried out to the surface of a stacked body for aflexible display device, the surface of the stacked body for a flexibledisplay device is electrified by the friction of the eraser. The layerconstituting the stacked body for a flexible display device may bedeteriorated and an electrification damage may occur when the chargedelectricity is discharged. When such an electrification damage occurs,the surface condition of the stacked body for a flexible display deviceis believed to be changed so that the abrasion resistance is decreasedin some cases. In contrast to this, in the present disclosure, since thesurface resistance of the antistatic layer side surface of the stackedbody for a flexible display device after the eraser test is apredetermined value or less, the electrification of the antistatic layerside surface of the stacked body for a flexible display device by theeraser test is believed to be suppressed, so that the deterioration ofthe layer or the electrification damage described above may besuppressed. As the result, excellent abrasion resistance is presumed tobe obtained.

Also, in the present disclosure, since the initial contact angle withrespect to water, of the antistatic layer side surface of the stackedbody for a flexible display device, is a predetermined value or more;and since the ratio of a contact angle with respect to water after asteel wool test, with respect to an initial contact angle with respectto water, is a predetermined value or more, excellent abrasionresistance with respect to a relatively hard matter such as an itemstored in the pockets of clothing or a bag may be obtained.

Further, in the present disclosure, since surface resistance of theantistatic layer side surface of the stacked body for a flexible displaydevice after an eraser test is a predetermined value or less, forexample, excellent abrasion resistance with respect to a relatively softmatter such as a stylus pen, a finger, cloth of clothing or a bag may beobtained.

Also, in the present disclosure, since the abrasion resistance may beeasily inferred from the initial surface resistance before an erasertest, a target abrasion resistance for the stacked body for a flexibledisplay device may be easily designed.

Each constitution of the stacked body for a flexible display device inthe present disclosure is hereinafter described.

1. Properties of Stacked Body for Flexible Display Device

In the present disclosure, the contact angle with respect to water, ofthe antistatic layer side surface of the stacked body for a flexibledisplay device, is 100° or more. By the initial contact angle withrespect to water being in the range, sufficient antifouling property maybe obtained, thereby, adhesion of fingerprint or dirt may be suppressed,and even when the fingerprint or dirt is adhered, it may be easily wipedoff. Also, the initial contact angle with respect to water ispreferably, for example, 150° or less.

Also, in the present disclosure, the contact angle with respect to waterafter a steel wool test, of the antistatic layer side surface of thestacked body for a flexible display device is preferably, for example,100° or more; wherein, in the steel wool test, the antistatic layer sidesurface of the stacked body for a flexible display device is rubbed witha #0000 steel wool, for 2500 strokes, applying a load of 9.8 N. By thecontact angle with respect to water after the steel wool test being inthe range, excellent abrasion resistance may be obtained as well asexcellent antifouling property may be maintained. Also, the contactangle with respect to water after the steel wool test is preferably, forexample, 150° or less.

Also, the ratio of the contact angle with respect to water after thesteel wool test, with respect to an initial contact angle with respectto water, of the antistatic layer side surface of the stacked body for aflexible display device, is 0.6 or more, preferably 0.8 or more, andmore preferably 0.9 or more. By the ratio of the contact angle withrespect to water being in the range, abrasion resistance may beimproved. Also, since the contact angle with respect to water tends tobe decreased after the steel wool test, the ratio of the contact anglewith respect to water may be, for example, 1.0 or less.

The ratio of the contact angle with respect to water may be determinedfrom the following formula wherein the initial contact angle, withrespect to water, of an antistatic layer side surface of the stackedbody for a flexible display device before the steel wool test isregarded as “A”; and the contact angle, with respect to water, of anantistatic layer side surface of the stacked body for a flexible displaydevice after the steel wool test is regarded as “B”.

Ratio of contact angle with respect to water=B/A

Here, the steel wool test may be carried out by the following procedure.That is, using #0000 steel wool, the steel wool is fixed to a 2 cm×2 cmjig, the antistatic layer side surface of the stacked body for aflexible display device is rubbed for 2500 strokes, applying a load of9.8 N, at traveling speed of 140 mm/sec and traveling distance of 70 mm.As the #0000 steel wool, Bonstar #0000 from Nippon Steel Wool Co., Ltd.may be used. Also, as a tester, for example, Color Fastness RubbingTester AB-301 from Tester Sangyo Co., Ltd. may be used. Incidentally,the steel wool test is carried out under the condition wherein a stackedbody for a flexible display device having a size of, for example, 5cm×10 cm is fixed on a glass plate with Cellotape (registered trademark)from Nichiban Co., Ltd. so that there is no bend or wrinkle.

Also, the contact angle with respect to water may be measured by asessile drop method according to JIS R3257: 1999. Specifically, 2 ml ofwater is dropped on the antistatic layer side surface of the stackedbody for a flexible display device, and the contact angle immediatelyafter the drop is measured. The contact angle with respect to water ofthe antistatic layer side surface of the stacked body for a flexibledisplay device is measured at ten places, and the arithmetic averagevalue of the measurement value of the ten places is regarded as thecontact angle with respect to water. As the measurement device, forexample, a contact angle meter DropMaster 300 from Kyowa InterfaceScience Co., Ltd. may be used.

In the present disclosure, the surface resistance of the antistaticlayer side surface of the stacked body for a flexible display device is9×10¹³Ω/□ or less, preferably 9×10¹²Ω/□ or less. By the initial surfaceresistance being in the range, the surface resistance of the antistaticlayer side surface of the stacked body for a flexible display deviceafter a predetermined eraser test tends to be in a predetermined rangeso that excellent abrasion resistance is presumed to be obtained. Also,when the initial surface resistance is in the range, excellentantistatic property may be obtained.

Also, in the present disclosure, the surface resistance, of theantistatic layer side surface of the stacked body for a flexible displaydevice, after an eraser test is 9×10¹³Ω/□ or less, preferably 5×10¹³Ω/□or less, and more preferably 9×10¹²Ω/□ or less; wherein, in the erasertest, the antistatic layer side surface of the stacked body for aflexible display device is rubbed with a 6 mm diameter eraser, for 2500strokes, applying a load of 9.8 N. By the surface resistance after theeraser test being in the range, excellent abrasion resistance may beobtained as well as excellent antistatic property may be maintained.

Also, the ratio of the surface resistance of the antistatic layer sidesurface of the stacked body for a flexible display device after theeraser test, with respect to an initial surface resistance, ispreferably, for example, 20.0 or less, more preferably 10.0 or less, andfurther preferably 5.0 or less. By the ratio of the surface resistancebeing in the range, the abrasion resistance may be improved. The reasontherefor is not clear, but presumed as follows. That is, the ratio ofthe surface resistance is high when, for example, the initial surfaceresistance is low and the surface resistance after the eraser test ishigh. Meanwhile, the ratio of the surface resistance is low when, forexample, the initial surface resistance is low and the surfaceresistance after the eraser test is also low. In the latter case, it isbelieved that the surface of the stacked body for a flexible displaydevice is not likely to be electrified by the friction of the eraser sothat electrification damage is not likely to occur. Therefore, by theratio of the surface resistance being low as in the range, it isbelieved that the electrification of the antistatic layer side surfaceof the stacked body for a flexible display device by the eraser test mayfurther by suppressed so that the electrification damage may further besuppressed. As the result, the abrasion resistance is presumed to beimproved. Also, since the surface resistance tend to be increased afterthe eraser test, the ratio of the surface resistance may be, forexample, 1.0 or more.

The ratio of the surface resistance may be determined from the followingformula wherein the initial surface resistance of the antistatic layerside surface of the stacked body for a flexible display device beforethe eraser test is regarded as “C”; and the surface resistance of theantistatic layer side surface of the stacked body for a flexible displaydevice after the eraser test is regarded as “D”.

Ratio of surface resistance=D/C

Here, the eraser test may be carried out by the following procedure.That is, using a 6 mm diameter eraser, the eraser is inserted into a jigprovided with a 6 mm diameter hole so that 4 mm of the tip of the eraseris exposed from the jig, the jig with the eraser is installed into acolor fastness rubbing tester, and the antistatic layer side surface ofthe stacked body for a flexible display device is rubbed for 2500strokes, with the eraser, applying a load of 9.8 N and at travelingspeed of 80 mm/sec. As the 6 mm diameter eraser, for example, 6 mmdiameter eraser from Minoan Co., Ltd. may be used. Also, as a colorfastness rubbing tester, for example, Color Fastness Rubbing TesterAB-301 from Tester Sangyo Co., Ltd. may be used.

Also, the surface resistance may be measured by using Hiresta-UX MCP-HTtype from Nittoseiki Analytech Co., Ltd. as a resistivity meter, usingMCP-H1014 URS probe as a probe after the eraser test, using MCP-HTP11 UAprobe for the initial before the eraser test, and at applied voltage of1000 V. Also, the surface resistance of the antistatic layer sidesurface of the stacked body for a flexible display device is measured atten places, and the arithmetic average value of the measurement value ofthe ten places is regarded as the surface resistance. Incidentally, whenmeasuring the surface resistance, the measurement is carried out afterleaving the stacked body for a flexible display device to stand for 1hour under environment of temperature of 23±2° C., and humidity of50±10%.

Also, in the present disclosure, the average value of the friction forcewith respect to the eraser, of the antistatic layer side surface of thestacked body for a flexible display device is preferably, for example,0.98 N or more and 9.80 N or less, more preferably 1.96 N or more and8.80 N or less, further preferably 2.45 N or more and 7.80 N or less.When the average value of the initial friction force with respect to theeraser is in the range, the abrasion resistance may be increased.

Also, in the present disclosure, the maximum value of the friction forcewith respect to the eraser, of the antistatic layer side surface of thestacked body for a flexible display device, after an eraser test ispreferably, for example, 0.98 N or more and 9.80 N or less, morepreferably 1.96 N or more and 8.80 or less, and further preferably 2.45N or more and 7.80 N or less, wherein, in the eraser test, theantistatic layer side surface of the stacked body for a flexible displaydevice is rubbed with a 6 mm diameter eraser, for 2500 strokes, applyinga load of 9.8 N. By the friction force with respect to the eraser, afterthe eraser test being in the range, excellent abrasion resistance may beobtained as well as excellent antistatic property may be maintained.

Also, the ratio of the maximum value of the friction force with respectto the eraser after the eraser test, with respect to the average valueof the initial friction force with respect to the eraser, of theantistatic layer side surface of the stacked body for a flexible displaydevice is preferably, for example, 1.50 or less, more preferably 1.48 orless, and further preferably 1.45 or less. By the ratio of the frictionforce with respect to the eraser being in the range, the abrasionresistance may be improved. Also, the ratio of the friction force withrespect to the eraser may be, for example, 1.00 or more.

The ratio of the friction force with respect to the eraser may bedetermined from the following formula wherein the average value ofinitial friction force with respect to the eraser, of the antistaticlayer side surface of the stacked body for a flexible display devicebefore the eraser test is regarded as “E”; and the maximum value of thefriction force with respect to the eraser, of the antistatic layer sidesurface of the stacked body for a flexible display device, after theeraser test is regarded as “F”.

Ratio of friction force=F/E

Here, the friction force with respect to the eraser may be measured byusing a 6 mm diameter eraser, inserting the eraser into a jig providedwith a 6 mm diameter hole so that 4 mm of the tip of the eraser isexposed from the jig, installing the jig with the eraser into a frictionmeasurement device, and rubbing the antistatic layer side surface of thestacked body for a flexible display device with the eraser, applying aload of 1.96 N and at traveling speed of 840 ram/min. As the 6 mmdiameter eraser, for example, 6 mm diameter eraser from Minoan Co., Ltd.may be used. Also, as a friction measurement device, for example,TriboGear Type 18 from Shinto Scientific Co., Ltd. may be used.Specifically, as shown in FIG. 2 , the eraser test described above isfirstly carried out to a part of antistatic layer side surface 30 of thestacked body for a flexible display device 1, and eraser tested portion32 having a rectangular shape is formed. Then, using the eraser, theantistatic layer side surface 30 of the stacked body for a flexibledisplay device 1 is rubbed, as shown with an arrow, in the order oferaser test-untested portion 31, eraser tested portion 32, and erasertest-untested portion 31 to measure the friction force. In doing so, asshown with an arrow, the eraser is moved vertically to the longitudinaldirection of the rectangle eraser tested portion 32. The average valueof the friction force with respect to the eraser of the erasertest-untested portion may be regarded as the average value of theinitial friction force with respect to the eraser, and the maximum valueof the friction force with respect to the eraser of the eraser testedportion may be regarded as the maximum value of the friction force withrespect to the eraser after the eraser test. Also, as shown in FIG. 2 ,when the point at which the friction force with respect to the eraser isthe maximum in the eraser tested portion 32 is regarded as 0 mm, theaverage value of the initial friction force with respect to the erasertest is regarded as the average value of the friction force in theeraser test-untested portion 31, in a range of 4.2 mm to 9.8 mm on thebasis of the point (0 mm) described above.

The total light transmittance of the stacked body for a flexible displaydevice in the present disclosure is preferably, for example, 85% ormore, more preferably 88% or more, and further preferably 90% or more.By having such a high total light transmittance, a stacked body for aflexible display device having excellent transparency may be obtained.

Here, the total light transmittance of the stacked body for a flexibledisplay device may be measured according to JIS K-7361-1: 1997, and maybe measure with, for example, with a haze meter HM150 from MurakamiColor Research Laboratory Co., Ltd.

The haze of the stacked body for a flexible display device in thepresent disclosure is preferably, for example 5% or less, morepreferably 2% or less, and further preferably 1% or less. By having sucha low haze, a stacked body for a flexible display device havingexcellent transparency may be obtained.

Here, the haze of the stacked body for a flexible display device may bemeasured according to JIS K-7136: 2000, and may be measure with, forexample, with a haze meter HM150 from Murakami Color Research LaboratoryCo., Ltd.

The stacked body for a flexible display device in the present disclosurepreferably has a bending resistance. Specifically, when the dynamicbending test described below is carried out to the stacked body for aflexible display device repeatedly for 200,000 times, it is preferablethat a crack or a fracture does not occur in the stacked body for aflexible display device, and it is more preferable that a crack or afracture does not occur in the stacked body for a flexible displaydevice when the dynamic bending test is carried out repeatedly for500,000 times.

In the dynamic bending test, the stacked body for a flexible displaydevice may be folded so that the antistatic layer faces outward, or thestacked body for a flexible display device may be folded so that theantistatic layer faces inward; and in either of these cases, it ispreferable that a crack or a fracture does not occur in the stacked bodyfor a flexible display device.

The dynamic bending test is carried out as follows. Firstly, a stackedbody for a flexible display device having a size of 20 mm×100 mm isprepared. Then, in the dynamic bending test, as shown in FIG. 3A, shortside portion 1C and short side portion 1D opposing to the short sideportion 1C of the stacked body for a flexible display device 1 arerespectively fixed by parallelly arranged fixing portions 51. Also, asshown in FIG. 3A, the fixing portions 51 are movable by sliding inhorizontal direction. Then, as shown in FIG. 3B, by moving the fixingportions 51 so as to be closer to each other, the stacked body for aflexible display device 1 is deformed so as to be folded. Further, asshown in FIG. 3C, after moving the fixing portions 51 to the positionwherein distance “d” between the two opposing short side portions 1C and1D of the stacked body for a flexible display device 1 fixed by thefixing portions 51 is 30 mm, the deformation of the stacked body for aflexible display device 1 is dissolved by moving the fixing portions 51in opposite directions. As shown in FIGS. 3A to 3C, by moving the fixingportions 51, the stacked body for a flexible display device 1 may befolded into 180°. Also, by carrying out the dynamic bending test so thatbent portion 1E of the stacked body for a flexible display device 1 doesnot protrude from the lower end edge of the fixing portions 51, and bycontrolling the distance when the fixing portions 51 are the closest,distance “d” between the two opposing short side portions 1C and 1D ofthe stacked body for a flexible display device 1 may be 30 mm. In thiscase, the outer diameter of the bent portion 1E is regarded as 30 mm.

In the stacked body for a flexible display device, it is preferable thata crack or a fracture does not occur when the dynamic bending testwherein the stacked body for a flexible display device 1 is folded into180° so that the distance “d” between the opposing short side portions1C and 1D of the stacked body for a flexible display device 1 is 30 mm,is carried out repeatedly for 200,000 times; among the above, it ispreferable that a crack or a fracture does not occur when the dynamicbending test wherein the stacked body for a flexible display device 1 isfolded into 180° so that the distance “d” between the opposing shortside portions 1C and 1D of the stacked body for a flexible displaydevice is 20 mm, is carried out repeatedly for 200,000 times;particularly, it is preferable that a crack or a fracture does not occurwhen the dynamic bending test wherein the stacked body for a flexibledisplay device 1 is folded into 180° so that the distance “d” betweenthe opposing short side portions 1C and 1D of the stacked body for aflexible display device 1 is 10 mm, is carried out repeatedly for200,000 times.

2. Antistatic Layer

The antistatic layer in the present disclosure is placed on one surfaceside of the substrate layer, and is a layer configured to impart anantistatic property to the stacked body for a flexible display device.

The antistatic layer is not particularly limited as long as it has anantistatic property, and may include at least an antistatic agent. Also,the antistatic layer may include, for example, an antistatic agent and aresin.

As the antistatic agent, for example, either one of a low molecularweight type antistatic agent, and a polymer type antistatic agent may beused. Also, examples of the antistatic agent may include an ionconductive type antistatic agent, and an electron conductive typeantistatic agent. One kind of the antistatic agent may be used alone,and two kind or more may be used in combination.

Examples of the ion conductive type antistatic agent may includecationic antistatic agents such as quaternary ammonium salts, andpyridium salts; anionic antistatic agents such as alkali metal salts of,for example, sulfonic acids, phosphoric acids, and carboxylic acids suchas lithium salts, sodium salts, and potassium salts; amphotericantistatic agents such as amino acid based, and amino acid sulfate esterbased; nonionic antistatic agents such as amino alcohol based, glycerinbased, and polyethylene glycol based; and ionic liquids. Among these, aquaternary ammonium salt or a lithium salt is preferable since itexhibits excellent compatibility with a resin.

Examples of the electron conductive type antistatic agent may includeconductive polymers such as polyacetylene based, and polythiophenebased; conductive particles such as metal particles, metal oxideparticles, and carbon nanotubes; and conductive fibers. Also, anantistatic agent obtained by combining a dopant with a conductivepolymer such as polyacetylene and polythiophene; or an antistatic agentwherein conductive particles are included in the conductive polymer, maybe used. Among them, a conductive polymer is preferable from theviewpoint of maintaining the antistatic property.

Specific examples of the conductive polymer may include conductivepolymers such as polyacetylene, polyaniline, polythiophene, polypyrrole,polyphenylene sulfide, poly(1,6-heptadiyne), polybiphenylene(polyparaphenylene), polyparaphenylene sulfide, polyphenylacetylene,poly(2,5-thienylene), and derivatives thereof. Preferable examplesthereof may include polythiophene based conductive polymers such as3,4-ethylenedioxythiophene (PEDOT). By using the conductive polymer asthe antistatic agent, the antistatic property may be maintained for along period of time.

Examples of the metal constituting the fine metal particles may includeAu, Ag, Cu, Al, Fe, Ni, Pd, and Pt themselves, or an alloy of thesemetals.

The metal oxide constituting the metal oxide particles is notparticularly limited, and examples thereof may include tin oxide,antimony oxide, antimony doped tin oxide (ATO), tin doped indium oxide(ITO), aluminum doped zinc oxide (AZO), fluorine doped tin oxide (FTO),and zinc oxide (ZnO). Among them, antimony doped tin oxide (ATO) ispreferable from the viewpoint of exhibiting excellent antistaticproperty. Also, among ATO, a chain-like ATO wherein a plurality of ATOparticles are connected, is preferable.

Among the antistatic agents described above, an antistatic agent that isnot particulate is preferable. This is because the antistatic agentother than the particulate antistatic agent tends to maintain theantistatic property as compared with the particulate antistatic agent.In particular, the antistatic agent is preferably a polymer typeantistatic agent. This is because the polymer type antistatic agent mayimpart antistatic property even in a small amount, and is able tomaintain optical properties and hardness.

The content of the antistatic agent is not particularly limited as longas it is an amount capable of obtaining the antistatic layer satisfyingthe surface resistance described above, and is appropriately selectedaccording to, for example, the material of the antistatic layer.

For example, when the antistatic layer includes an antistatic agent anda resin, the amount is preferably 0.1 parts by mass or more and 100parts by mass or less, more preferably 0.2 parts by mass or more and 50parts by mass or less, and further preferably 0.3 parts by mass or moreand 20 parts by mass or less, with respect to 100 parts by mass of theresin component. When the content of the antistatic agent is too low,there may be cases where sufficient antistatic property may not beimparted to the antistatic layer; or an antistatic layer satisfying thesurface resistance described above may not be obtained. Also, when thecontent of the antistatic agent is too high, it may be difficult to formthe antistatic layer, or the abrasion resistance may be lowered.

The resin may be appropriately selected according to the performance tobe imparted to the antistatic layer.

For example, when the antistatic layer is not required to have a hardcoating property, examples of the resin may include at least one kindselected from the group consisting of (meth)acrylic based resins,cellulose based resins, urethane based resins, vinyl chloride basedresins, polyester based resins, polyolefin based resins, polycarbonates,nylons, polystyrenes, and ABS resins. Among them, for example,(meth)acrylic based resins, and polyester based resins are preferablefrom the viewpoint of ease of processing and hardness.

Examples of the (meth)acrylic based resin may include polymethylmethacrylate. Also, examples of the cellulose based resin may includediacetyl cellulose, cellulose acetate propionate (CAP), and celluloseacetate butyrate (CAB). Examples of the urethane based resin may includeurethane resins. Examples of the vinyl chloride based resin may includepolyvinyl chloride, and a vinyl chloride-vinyl acetate copolymer. Also,examples of the polyester based resin may include polyethyleneterephthalate. Also, examples of the polyolefin based resin may includepolyethylene, and polypropylene.

Also, for example, when the antistatic layer has a hard coatingproperty, specific examples of the resin may include a cured product ofa polymerizable compound. The cured product of a polymerizable compoundmay be obtained by carrying out a polymerization reaction of apolymerizable compound, by a known method using a polymerizationinitiator according to the needs.

The polymerizable compound includes at least one polymerizablefunctional group in the molecule. As the polymerizable compound, forexample, at least one kind of radical polymerizable compound and cationpolymerizable compound may be used.

The radical polymerizable compound is a compound including a radicalpolymerizable group. The radical polymerizable group included in theradical polymerizable compound may be any functional group capable ofgenerating a radical polymerization reaction, and is not particularlylimited; and examples thereof may include a group including acarbon-carbon unsaturated double bond, and specific examples thereof mayinclude a vinyl group and a (meth) acryloyl group. Incidentally, whenthe radical polymerizable compound includes two or more radicalpolymerizable groups, these radical polymerizable groups may be thesame, and may be different from each other.

The number of radical polymerizable groups included in one molecule ofthe radical polymerizable compound is preferably two or more, and morepreferably three or more, from the viewpoint of increasing the hardnessof the antistatic layer so that the steel wool resistance is improved.

Among the above, from the viewpoint of high reactivity, the radicalpolymerizable compound is preferably a compound including a (meth)acryloyl group. For example, a polyfunctional (meth) acrylate monomerand oligomer having a molecular weight of several hundred to severalthousand, and including several (meth) acryloyl groups in the moleculemay be preferably used; such as those referred to as urethane(meth)acrylate, polyester (meth)acrylate, epoxy (meth)acrylate, melamine(meth) acrylate, polyfluoroalkyl (meth) acrylate, and silicone(meth)acrylate; and a polyfunctional (meth) acrylate polymer includingtwo or more (meth) acryloyl groups on the side chain of an acrylatepolymer may also be preferably used. Among the above, a polyfunctional(meth) acrylate monomer including two or more (meth) acryloyl groups inone molecule may be preferably used. By the antistatic layer including acured product of the polyfunctional (meth) acrylate monomer, thehardness of the antistatic layer may be increased so that the steel woolresistance may be improved. Further, the close adhesiveness may also beimproved. Also, a polyfunctional (meth) acrylate oligomer or polymerincluding two or more (meth) acryloyl groups in one molecule may also bepreferably used. By the antistatic layer including a cured product ofthe polyfunctional (meth) acrylate oligomer or polymer, the hardness ofthe antistatic layer may be increased so that the steel wool resistancemay be improved. Further, the bending resistance and close adhesivenessmay also be improved.

Incidentally, in the present specification, (meth) acryloyl representseach of acryloyl and methacryloyl, and (meth) acrylate represents eachof acrylate and methacrylate.

Specific examples of the polyfunctional (meth)acrylate monomer mayinclude those described in, for example, JP-A No. 2019-132930. Amongthem, those having 3 or more and 6 or less (meth)acryloyl groups in onemolecule are preferable from the viewpoint of high reactivity, highhardness of the antistatic layer, and improvement of the steel woolresistance. As such a polyfunctional (meth)acrylate monomer, forexample, pentaerythritol triacrylate (PETA), dipentaerythritolhexaacrylate (DPHA), pentaerythritol tetraacrylate (PETTA),dipentaerythritol pentaacrylate (DPPA), trimethylolpropanetri(meth)acrylate, tripentaerythritol octa(meth)acrylate, andtetrapentaerythritol deca(meth)acrylate may be preferably used. Inparticular, at least one kind selected from pentaerythritoltri(meth)acrylate, dipentaerythritol penta(meth)acrylate, anddipentaerythritol hexaacrylate is preferable.

Also, when the radical polymerizable compound is used, the steel woolresistance may be decreased due to the flexible group in the molecularstructure. Therefore, in order to suppress the decrease in steel woolresistance due to the flexible components (soft segments), it ispreferable to use a radical polymerizable compound wherein a flexiblegroup is not introduced into the molecular structure. Specifically, itis preferable to use a radical polymerizable compound that is not EO orPO modified. By using such a radical polymerizable compound, thecrosslinking point may be increased and the steel wool resistance may beimproved.

In order to adjust the hardness or viscosity, or to improve the closeadhesiveness, the antistatic layer may include a monofunctional (meth)acrylate monomer as the radical polymerizable compound. Specificexamples of the monofunctional (meth) acrylate monomer may include thosedescribed in, for example, Japanese Patent Application Laid-Open (JP-A)No. 2019-132930.

The cation polymerizable compound is a compound including a cationpolymerizable group. The cation polymerizable group included in thecation polymerizable compound may be a functional group capable ofgenerating a cation polymerization reaction, and is not particularlylimited; and examples thereof may include an epoxy group, an oxetanylgroup, and a vinyl ether group. Incidentally, when the cationpolymerizable compound includes two or more cation polymerizable groups,these cation polymerizable groups may be the same, and may be differentfrom each other.

The number of the cation polymerizable groups included in one moleculeof the cation polymerizable compound is preferably two or more, and morepreferably three or more, from the viewpoint of increasing the hardnessof the antistatic layer so that the steel wool resistance is improved.

Also, among the above, as a cation polymerizable compound, a compoundincluding at least one kind of an epoxy group and an oxetanyl group as acation polymerizable group is preferable, and a compound including twoor more of at least one kind of an epoxy groups and an oxetanyl groupsin one molecule is more preferable. A cyclic ether group such as anepoxy group and an oxetanyl group is preferable from the viewpoint thatshrinkage associated with the polymerization reaction is small. Also, acompound including the epoxy group among the cyclic ether groups hasadvantages in that compounds having various structure may be easilyobtained; the durability of the obtained antistatic layer is notadversely affected; and the compatibility with the radical polymerizablecompound may be easily controlled. Also, the oxetanyl group among thecyclic ether groups has advantaged in that the degree of polymerizationis high compared with the epoxy group; the toxicity is low; and when theobtained antistatic layer is combined with a compound including an epoxygroup, the network forming rate obtained from the cationic polymerizablecompound in the coating film is accelerated, and an independent networkis formed without leaving unreacted monomers in the film even in aregion mixed with the radical polymerizable compound.

Examples of the cationic polymerizable compound including an epoxy groupmay include an alicyclic epoxy resins such as polyglycidyl ether of apolyhydric alcohol including an alicyclic ring, or resins obtained byepoxidizing a compound including a cyclohexene ring or a cyclopentenering, with a suitable oxidizing agent such as hydrogen peroxide and aperacid; an aliphatic epoxy resins such as polyglycidyl ether ofaliphatic polyhydric alcohol or alkylene oxide adduct thereof,polyglycidyl ester of aliphatic long-chain polybasic acid, orhomopolymer or copolymer of glycidyl (meth)acrylate; a glycidyl ethertype epoxy resin such as glycidyl ether produced by the reaction ofbisphenols such as bisphenol A, bisphenol F, and hydrogenated bisphenolA, or derivative thereof such as alkylene oxide adduct and caprolactoneadduct with epichlorohydrin, and resins that is novolac epoxy resin andderived from bisphenols.

Specific examples of the cationic polymerizable compound including thealicyclic epoxy resin, the glycidyl ether type epoxy resin, and anoxetanyl group may include those described in, for example, JP-A No.2018-104682.

Among them, since the antistatic layer preferably has a hard coatingproperty, the resin is preferably a cured product of a polymerizablecompound. When the antistatic layer has a hard coating property, thecontact angle with respect to water after the steel wool test describedabove may be satisfied on the antistatic layer side surface of thestacked body for a flexible display device.

The antistatic layer may include a polymerization initiator ifnecessary. The polymerization initiator may be used by appropriatelyselecting from, for example, a radical polymerization initiator, acation polymerization initiator, and a radical and cation polymerizationinitiator. These polymerization initiators are decomposed by at leastone kind of light irradiation and heating to generate radicals orcations to cause radical polymerization and cation polymerization toproceed. Incidentally, all of the polymerization initiator may bedecomposed and may not be left in the antistatic layer, in some cases.

The antistatic layer preferably includes an antifoulant. The stackedbody for a flexible display device may be imparted with an antifoulingproperty. When the antistatic layer includes the antifoulant, theantistatic layer side surface of the stacked body for a flexible displaydevice may satisfy the contact angle with respect to water describedabove.

The antifoulant is not particularly limited, and examples thereof mayinclude a silicone based antifoulant, a fluorine based antifoulant, anda silicone based-fluorine based antifoulant. Also, the antifoulant maybe an acrylic based antifoulant. One kind of the antifoulant may be usedalone, and two kinds or more may be used as a mixture.

A fingerprint is not likely to be marked (inconspicuous) on theantistatic layer including a silicone based antifoulant or a fluorinebased antifoulant, and is easily wiped off. Also, When the siliconeantifoulant or the fluorine antifoulant is included, since the surfacetension when applying a composition for an antistatic layer may bedecreased, the leveling property is excellent, so that the appearance ofthe obtained antistatic layer will be excellent.

Also, the antistatic layer including the silicone based antifoulant isexcellent in the sliding property, and excellent in scratch resistance.In a flexible display device provided with a stacked body for a flexibledisplay device including an antistatic layer including such a siliconebased antifoulant, since the sliding property when it is touched with afinger or a stylus pen is excellent, the texture is improved.

As the antifoulant, in order to improve the durability of theantifouling performance, an antifoulant including a reactive functionalgroup is preferably used. That is, the antistatic layer preferablyincludes a cured product of a resin composition including an antifoulantincluding the polymerizable compound described above, and a reactivefunctional group. By using the antifoulant including the reactivefunctional group, the antifouling performance may be maintained alsoafter the steel wool test and the eraser test, so that the steel woolresistance and the eraser resistance may be improved.

The number of the reactive functional groups included in the antifoulantmay be 1 or more, and preferably 2 or more. By using the antifoulantincluding 2 or more reactive functional groups, the scratch resistanceand the abrasion resistance may be improved.

The content of the antifoulant is not particularly limited as long as itis an amount capable of obtaining the antistatic layer satisfying thecontact angle with respect to water described above, and is preferably,for example, 0.01 parts by mass or more and 3.0 parts by mass or less,with respect to 100 parts by mass of the resin component. When thecontent of the antifoulant is too low, there may be cases wheresufficient antifouling property may not be imparted to the antistaticlayer. Also, when the content of the antifoulant is too high, thehardness of the antistatic layer is decreased so that the abrasionresistance may be decreased.

The antistatic layer may include an additive such as an inorganicparticle, an organic particle, an ultraviolet absorber, an antioxidant,a light stabilizer, an antiglare agent, a leveling agent, a surfactant,an easy lubricant, various sensitizers, a flame retardant, an adhesiveimparting agent, a polymerization inhibitor, and a surface modifier, ifnecessary.

The thickness of the antistatic layer is not particularly limited aslong as it is a thickness capable of obtaining an antistatic layersatisfying the surface resistance described above, and is preferably,for example, 0.5 μm or more and 50 μm or less, more preferably 1.0 μm ormore and 40 μm or less, and further preferably 1.5 μm or more and 30 μmor less. When the thickness of the antistatic layer is too thin,sufficient antistatic property may not be obtained. Also, when thethickness of the antistatic layer is too thick, the flexibility may bedeteriorated.

Here, the thickness of the antistatic layer may be the average value ofthe thickness of arbitrary 10 points obtained by measuring from thethickness directional cross-section of the stacked body for a flexibledisplay device by observing with a transmission electron microscope(TEM), a scanning electron microscope (SEM) or a scanning transmissionelectron microscope (STEM). Incidentally, the same may be applied to themeasuring methods of the thickness of other layers included in thestacked body for a flexible display device.

The antistatic layer may be placed on one surface side of the substratelayer; among the above, the antistatic layer is preferably placed on theoutermost surface in the stacked body for a flexible display device.This is because the surface resistance of the antistatic layer sidesurface of the stacked body for a flexible display device may be easilyadjusted to satisfy the surface resistance described above.

Examples of a method for forming an antistatic layer may include amethod wherein the substrate layer is coated with a composition for anantistatic layer.

3. Substrate Layer

The substrate layer in the present disclosure is a member configured tosupport the antistatic layer, and has transparency.

The substrate layer is not particularly limited as long as it hastransparency; and examples thereof may include a resin substrate, and aglass substrate.

(1) Resin Substrate

The resin constituting the resin substrate is not particularly limitedas long as it is able to obtain a resin substrate having transparency;and examples thereof may include a polyimide based resin, a polyamidebased resin, and a polyester based resin. Examples of the polyimidebased resin may include polyimide, polyamideimide, polyetherimide, andpolyesterimide. Examples of the polyester based resin may includepolyethylene terephthalate, polypropylene terephthalate, polybutyleneterephthalate, and polyethylene naphthalate. Among them, the polyimidebased resin, the polyamide based resin, or a mixture thereof ispreferable since it has bending resistance and has excellent hardnessand transparency, and the polyimide based resin is more preferable.

The polyimide based resin is not particularly limited as long as it isable to obtain a resin substrate having transparency; and among theabove, polyimide and polyamideimide are preferably used.

(a) Polyimide

The polyimide is obtained by reacting a tetracarboxylic acid componentand a diamine component. The polyimide is not particularly limited aslong as it satisfies the average value of the tensile storage elasticmodulus described above and has transparency; and it is preferable tohave at least one kind of the structure selected from the groupconsisting of the structure represented by the following general formula(1) and the following general formula (3), for example, from theviewpoint of having excellent transparency and excellent stiffness.

In the general formula (1), R¹ represents a tetravalent group which is atetracarboxylic acid residue; and R² represents at least one kind ofdivalent group selected from the group consisting of atrans-cyclohexanediamine residue, atrans-1,4-bismethylenecyclohexanediamine residue, a4,4′-diaminodiphenylsulfone residue, a 3,4′-diaminodiphenylsulfoneresidue, and a divalent group represented by the following generalformula (2). The “n” represents the number of repeating units, and is 1or more.

In the general formula (2), R³ and R⁴ each independently represents ahydrogen atom, an alkyl group, or a perfluoroalkyl group.

In the general formula (3), R⁵ represents at least one kind oftetravalent group selected from the group consisting of a cyclohexanetetracarboxylic acid residue, a cyclopentanetetracarboxylic acidresidue, a dicyclohexane-3,4,3′,4′-tetracarboxylic acid residue, and a4,4′-(hexafluoroisopropylidene)diphthalic acid residue; and R⁶represents a divalent group which is a diamine residue. The “n′”represents the number of repeating units, and is 1 or more.

Incidentally, “tetracarboxylic acid residue” refers to a residueobtained by excluding four carboxyl groups from a tetracarboxylic acid;and represents the same structure as a residue obtained by excluding anacid dianhydride structure from a tetracarboxylic acid dianhydride.Also, “diamine residue” refers to a residue obtained by excluding twoamino groups from a diamine.

In the general formula (1), R¹ is a tetracarboxylic acid residue, andmay be a residue obtained by excluding an acid dianhydride structurefrom a tetracarboxylic acid dianhydride. Examples of the tetracarboxylicacid dianhydride may include those described in WO 2018/070523. Amongthem, R¹ in the general formula (1) preferably includes at least onekind selected from the group consisting of a4,4′-(hexafluoroisopropylidene)diphthalic acid residue, a3,3′,4,4′-biphenyltetracarboxylic acid residue, pyromellitic acidresidue, a 2,3′,3,4′-biphenyltetracarboxylic acid residue, a3,3′,4,4′-benzophenone tetracarboxylic acid residue, a3,3′,4,4′-diphenylsulfone tetracarboxylic acid residue, a4,4′-oxydiphthalic acid residue, a cyclohexane tetracarboxylic acidresidue, and a cyclopentane tetracarboxylic acid residue from theviewpoint of improved transparency and improved stiffness. It is furtherpreferable to include at least one kind selected from the groupconsisting of a 4,4′-(hexafluoroisopropylidene)diphthalic acid residue,a 4,4′-oxydiphthalic acid residue and a 3,3′,4,4′-diphenylsulfonetetracarboxylic acid residue.

In R¹, these preferable residues are preferably included in total of 50mol % or more, more preferably 70 mol % or more, and further preferably90 mol % or more.

Also, as R¹, it is also preferable to use a mixture of the followings: atetracarboxylic acid residue group (Group A) suitable for improvingrigidity such as at least one kind selected from the group consisting ofa 3,3′,4,4′-biphenyltetracarboxylic acid residue, a3,3′,4,4′-benzophenone tetracarboxylic acid residue, and a pyromelliticacid residue; and a tetracarboxylic acid residue group (Group B)suitable for improving transparency such as at least one kind selectedfrom the group consisting of a 4,4′-(hexafluoroisopropylidene)diphthalicacid residue, a 2,3′,3,4′-biphenyltetracarboxylic acid residue, a3,3′,4,4′-diphenylsulfone tetracarboxylic acid residue, a4,4′-oxydiphthalic acid residue, a cyclohexane tetracarboxylic acidresidue, and a cyclopentanetetracarboxylic acid residue.

In this case, in relation to the content ratio of the tetracarboxylicacid residue group suitable for improving the rigidity (Group A) and thetetracarboxylic acid residue group suitable for improving transparency(Group B), with respect to 1 mol of the tetracarboxylic acid residuegroup suitable for improving transparency (Group B), the tetracarboxylicacid residue group suitable for improving rigidity (Group A) ispreferably 0.05 mol or more and 9 mol or less, more preferably 0.1 molor more and 5 mol or less, and further preferably 0.3 mol or more and 4mol or less.

Among them, R² in the general formula (1) is preferably at least onekind of divalent group selected from the group consisting of a4,4′-diaminodiphenylsulfone residue, a 3,4′-diaminodiphenylsulfoneresidue, and a divalent group represented by the general formula (2);and is further preferably at least one kind of divalent group selectedfrom the group consisting of a 4,4′-diaminodiphenylsulfone residue, a3,4′-diaminodiphenylsulfone residue, and a divalent group represented bythe general formula (2) wherein R³ and R⁴ are a perfluoroalkyl group,from the viewpoint of improved transparency and improved stiffness.

Among them, from the viewpoint of improved transparency and improvedstiffness, R⁵ in the general formula (3) preferably includes a4,4′-(hexafluoroisopropylidene) diphthalic acid residue, a3,3′,4,4′-diphenylsulfontetracarboxylic acid residue, and oxydiphthalicacid residue.

The R⁵ preferably includes 50 mol % or more, more preferably 70 mol % ormore, and further preferably 90 mol % or more of these preferableresidues.

The R⁶ in the general formula (3) is a diamine residue, and may be aresidue obtained by excluding two amino groups from a diamine. Examplesof the diamine may include those described in, for example, WO2018/070523. Among them, from the viewpoint of improved transparency andimproved stiffness, R⁶ in the general formula (3) preferably includes atleast one kind of divalent group selected from the group consisting of a2,2′-bis(trifluoromethyl)benzidine residue, abis[4-(4-aminophenoxy)phenyl]sulfone residue, a4,4′-diaminodiphenylsulfone residue, a2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane residue, abis[4-(3-aminophenoxy)phenyl]sulfone residue, a4,4′-diamino-2,2′-bis(trifluoromethyl)diphenylether residue, a1,4-bis[4-amino-2-(trifluoromethyl)phenoxy]benzene residue, a2,2-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropaneresidue, a 4,4′-diamino-2-(trifluoromethyl)diphenyl ether residue, a4,4′-diaminobenzanilide residue, aN,N′-bis(4-aminophenyl)terephthalamide residue and a9,9-bis(4-aminophenyl)fluorene residue; and further preferably includesat least one kind of divalent group selected from the group consistingof a 2,2′-bis(trifluoromethyl)benzidine residue, abis[4-(4-aminophenoxy)phenyl]sulfone residue, and a4,4′-diaminodiphenylsulfone residue.

In R⁶, these preferable residues are preferably included in total of 50mol % or more, more preferably 70 mol % or more, and further preferably90 mol % or more.

Also, as R⁶, it is also preferable to use a mixture of the followings: adiamine residue group (Group C) suitable for improving rigidity such asat least one kind selected from the group consisting of abis[4-(4-aminophenoxy)phenyl]sulfone residue, a 4,4′-diaminobenzanilideresidue, a N,N′-bis(4-aminophenyl) terephthalamide residue, aparaphenylenediamine residue, a metaphenylenediamine residue, and a4,4′-diaminodiphenylmethane residue; and a diamine residue group (GroupD) suitable for improving transparency such as at least one kindselected from the group consisting of a2,2′-bis(trifluoromethyl)benzidine residue, a 4,4′-diaminodiphenylsulfone residue, a 2,2-bis[4-(4-aminophenoxy)phenyl] hexafluoropropaneresidue, a bis[4-(3-aminophenoxy)phenyl]sulfone residue, a4,4′-diamino-2,2′-bis(trifluoromethyl)diphenylether residue, a1,4-bis[4-amino-2-(tirfluoromethyle)phenoxy] benzene residue, a2,2-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl] hexafluoropropaneresidue, a 4,4′-diamino-2(trifluoromethyl)dipenylether residue, and a9,9-bis(4-aminophenyl)fluorene residue.

In this case, in relation to the content ratio of the diamine residuegroup suitable for improving rigidity (Group C) and the diamine residuegroup suitable for improving transparency (Group D), with respect to 1mol of the diamine residue group suitable for improving transparency(Group D), the diamine residue group suitable for improving rigidity(Group C) is preferably 0.05 mol or more and 9 mol or less, morepreferably 0.1 mol or more and 5 mol or less, and further preferably 0.3mol or more and 4 mol or less.

In the structure represented by the general formula (1) and the generalformula (3), “n” and “n′” each independently represents the number ofrepeating units, and is 1 or more. The number of repeating units “n” inthe polyimide may be appropriately selected according to the structure,and is not particularly limited. The average number of repeating unitsmay be, for example, 10 or more and 2000 or less, and is preferably 15or more and 1000 or less.

Also, the polyimide may include a polyamide structure in a part thereof.Examples of the polyamide structure that may be included may include apolyamideimide structure including a tricarboxylic acid residue such astrimellitic acid anhydride; and a polyamide structure including adicarboxylic acid residue such as terephthalic acid.

From the viewpoint of improved transparency and improved surfacehardness, at least one of the tetravalent group which is atetracarboxylic acid residue of R¹ or R⁵, and the divalent group whichis a diamine residue of R² or R⁶ preferably includes an aromatic ring;and preferably includes at least one selected from the group consistingof (i) a fluorine atom, (ii) an aliphatic ring, and (iii) a structurewherein aromatic rings are connected to each other by an alkylene groupwhich may be substituted with a sulfonyl group or a fluorine. When thepolyimide includes at least one kind selected from a tetracarboxylicacid residue including an aromatic ring, and a diamine residue includingan aromatic ring, the molecular skeleton becomes rigid, the orientationproperty is increased, and the surface hardness is improved; however,the absorption wavelength of the rigid aromatic ring skeleton tends tobe shifted to the longer wavelength side, and the transmittance of thevisible light region tends to be decreased. Meanwhile, when thepolyimide includes (i) a fluorine atom, the transparency is improvedsince it may make the electronic state in the polyimide skeleton to astate wherein a charge transfer is difficult. Also, when the polyimideincludes (ii) an aliphatic ring, transparency is improved since thetransfer of charge in the skeleton may be inhibited by breaking theconjugation of n electrons in the polyimide skeleton. Also, when thepolyimide includes (iii) a structure wherein aromatic rings areconnected to each other by an alkylene group which may be substitutedwith a sulfonyl group or a fluorine, transparency is improved since thetransfer of charge in the skeleton may be inhibited by breaking theconjugation of n electrons in the polyimide skeleton.

Among them, from the viewpoint of improved transparency and improvedsurface hardness, at least one of the tetravalent group which is atetracarboxylic acid residue of R¹ or R⁵, and the divalent group whichis a diamine residue of R² or R⁶ preferably includes an aromatic ringand a fluorine atom; and the divalent group which is a diamine residueof R² or R⁶ preferably includes an aromatic ring and a fluorine atom.

Specific examples of such polyimide may include those having a specificstructure described in WO 2018/070523.

The polyimide may be synthesized by a known method. Also, a commerciallyavailable polyimide may be used. Examples of the commercially availableproducts of polyimide may include Neopulim (registered trademark) fromMitsubishi Gas Chemical Company, Inc.

The weight average molecular weight of the polyimide is preferably, forexample, 3000 or more and 500,000 or less, more preferably 5000 or moreand 300,000 or less, and further preferably 10,000 or more and 200,000or less. When the weight average molecular weight is too low, sufficientstrength may not be obtained, and when the weight average molecularweight is too high, the viscosity is increased and the solubility isdecreased, so that a substrate layer having a smooth surface and uniformthickness may not be obtained in some cases.

Incidentally, the weight average molecular weight of the polyimide maybe measured by gel permeation chromatography (GPC). Specifically, thepolyimide is used as a N-methylpyrrolidone (NMP) solution having aconcentration of 0.1% by mass; a 30 mmol % LiBr-NMP solution with awater content of 500 ppm or less is used as a developing solvent; andmeasurement is carried out using a GPC device (HLC-8120, used column:GPC LF-804 from SHODEX) from Tosoh Corporation, under conditions of asample injecting amount of 50 μL, a solvent flow rate of 0.4 mL/min, andat 37° C. The weight average molecular weight is determined on the basisof a polystyrene standard sample having the same concentration as thatof the sample.

(b) Polyamideimide

The polyamideimide is not particularly limited as long as it is able toobtain a resin substrate having transparency; and examples thereof mayinclude those having a first block including a constituent unit derivedfrom dianhydride, and a constituent unit derived from diamine; and asecond block including a constituent unit derived from aromaticdicarbonyl compound, and a constituent unit derived from aromaticdiamine. In the polyamideimide described above, the dianhydride mayinclude, for example, biphenyltetracarboxylic acid dianhydride (BPDA)and 2-bis(3,4-dicarboxyphenyl)hexafluoropropanedianhydride (6FDA). Also,the diamine may include bistrifluoromethylbenzidine (TFDB). That is, thepolyamideimide has a structure wherein a polyamideimide precursorincluding a first block wherein monomers including dianhydride anddiamine are copolymerized; and a second block wherein monomers includingan aromatic dicarbonyl compound and an aromatic diamine arecopolymerized, is imidized. By including the first block including animide bond and the second block including an amide bond, thepolyamideimide is excellent in not only optical properties but alsothermal and mechanical properties.

In particular, by using bistrifluoromethylbenzidine (TFDB) as thediamine forming the first block, thermal stability and opticalproperties may be improved. Also, by using2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) andbiphenyltetracarboxylic acid dianhydride (BPDA) as the dianhydrideforming the first block, birefringence may be improved, and heatresistance may be secured.

The dianhydride forming the first block comprises two kinds ofdianhydrides, that is, 6FDA and BPDA. In the first block, a polymer towhich TFDB and 6FDA are bonded, and a polymer to which TFDB and BPDA arebonded may be included, based on separate repeating units, respectivelysegmented; may be regularly arranged within the same repeating unit; andmay be included in a completely random arrangement.

Among the monomers forming the first block, BPDA and 6FDA are preferablyincluded as dianhydrides in a molar ratio of 1:3 to 3:1. This is becauseit is possible not only to secure the optical properties, but also tosuppress deterioration of mechanical properties and heat resistance, andit is possible to have excellent birefringence.

The molar ratio of the first block and the second block is preferably5:1 to 1:1. When the content of the second block is remarkably low, theeffect of improving the thermal stability and mechanical properties dueto the second block may not be sufficiently obtained in some cases.Also, when the content of the second block is higher than the content ofthe first block, although the thermal stability and mechanicalproperties may be improved, optical properties such as yellowness andtransmittance, may be deteriorated, and the birefringence property mayalso be increased in some cases. Incidentally, the first block and thesecond block may be random copolymers, and may be block copolymers. Therepeating unit of the block is not particularly limited.

Examples of the aromatic dicarbonyl compound forming the second blockmay include one kind or more selected from the group consisting ofterephthaloyl chloride (p-terephthaloyl chloride, TPC), terephthalicacid, iso-phthaloyl dichloride, and 4,4′-benzoyl dichloride(4,4′-benzoyl chloride). One kind or more selected from terephthaloylchloride (p-terephthaloyl chloride, TPC) and iso-phthaloyl dichloridemay be preferably used.

Examples of the diamine forming the second block may include diaminesincluding one kind or more flexible group selected from the groupconsisting of 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane(HFBAPP), bis(4-(4-aminophenoxy)phenyl)sulfone (BAPS),bis(4-(3-aminophenoxy)phenyl)sulfone (BAPSM), 4,4′-diaminodiphenylsulfone (4DDS), 3,3′-diaminodiphenyl sulfone (3DDS),2,2-bis(4-(4-aminophenoxy)phenylpropane (BAPP),4,4′-diaminodiphenylpropane (6HDA), 1,3-bis(4-aminophenoxy)benzene(134APB), 1,3-bis(3-aminophenoxy)benzene (133APB),1,4-bis(4-aminophenoxy)biphenyl (BAPB),4,4′-bis(4-amino-2-trifluoromethylphenoxy)biphenyl (6FAPBP),3,3-diamino-4,4-dihydroxydiphenylsulfone (DABS),2,2-bis(3-amino-4-hydroxyloxyphenyl)propane (BAP),4,4′-diaminodiphenylmethane (DDM), 4,4′-oxydianiline (4-CDA) and3,3′-oxydianiline (3-CDA).

When the aromatic dicarbonyl compound is used, it is easy to realizehigh thermal stability and mechanical properties, but may exhibit highbirefringence due to the benzene ring in the molecular structure.Therefore, in order to suppress the decrease in birefringence due to thesecond block, it is preferable to use a diamine wherein a flexible groupis introduced into the molecular structure. Specifically, the diamine ismore preferably one kind or more diamine selected frombis(4-(3-aminophenoxy)phenyl)sulfone (BAPSM),4,4′-diaminodiphenylsulfone (4DDS) and2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane (HFBAPP). Inparticular, the longer the length of the flexible group such as BAPSM,and a diamine including a substituent at meta position, the better thebirefringence may be exhibited.

For the polyamideimide precursor including a first block wherein adianhydride including a biphenyltetracarboxylic acid dianhydride (BPDA)and a 2-bis(3,4-dicarboxyphenyl)hexafluoropropanedianhydride (6FDA), anda diamine including bistrifluoromethylbenzidine (TFDB) arecopolymerized; and a second block wherein an aromatic dicarbonylcompound and an aromatic diamine are copolymerized, in the molecularstructure, the weight average molecular weight measured by GPC ispreferably, for example, 200,000 or more and 215,000 or less, and theviscosity is preferably, for example, 2400 poise or more and 2600 poiseor less.

The polyamideimide may be obtained by imidizing a polyamideimideprecursor. Also, a polyamideimide film may be obtained using thepolyamideimide. For a method for imidizing the polyamideimide precursorand a method for producing a polyamideimide film, JP-A No. 2018-506611,for example, may be referred.

(2) Glass Substrate

The glass constituting the glass substrate is not particularly limitedas long as it has transparency; and examples thereof may includesilicate glass and silica glass. Among them, borosilicate glass,aluminosilicate glass, and aluminoborosilicate glass are preferable, andalkali-free glass is more preferable. Examples of the commercialproducts of the glass substrate may include ultra-thin plate glassG-Leaf from Nippon Electric Glass Co., Ltd., and ultra-thin film glassfrom Matsunami Glass Ind., Ltd.

Also, the glass constituting the glass substrate is preferably achemically strengthened glass. The chemically strengthened glass ispreferable since it has excellent mechanical strength and may be madethin accordingly. The chemically strengthened glass is typically a glasswherein mechanical properties are strengthened by a chemical method bypartially exchanging ionic species, such as by replacing sodium withpotassium, in the vicinity of the surface of glass, and includes acompressive stress layer on the surface.

Examples of the glass constituting the chemically strengthened glasssubstrate may include aluminosilicate glass, soda-lime glass,borosilicate glass, lead glass, alkali barium glass, andaluminoborosilicate glass.

Examples of the commercial products of the chemically strengthened glasssubstrate may include Gorilla Glass from Corning Incorporated, andDragontrail from AGC Inc.

Among the above, as the substrate layer, a polyimide based resinsubstrate including a polyimide based resin or a glass substrate ispreferable. This is because it may be a substrate layer having bendingresistance and excellent hardness and transparency.

(3) Constitution of Substrate Layer

The thickness of the substrate layer is not particularly limited as longas it has a thickness capable of having flexibility, and isappropriately selected according to the type of the substrate layer.

The thickness of the resin substrate is preferably, for example, 10 μmor more and 100 μm or less, and more preferably 25 μm or more and 80 μmor less. When the thickness of the resin substrate is in the aboverange, excellent flexibility may be obtained, and at the same time,sufficient hardness may be obtained. It is also possible to suppresscurling of the stacked body for a flexible display device. Furthermore,it is preferable in terms of reducing the weight of the stacked body fora flexible display device.

The thickness of the glass substrate is preferably, for example, 200 μmor less, more preferably 15 μm or more and 100 μm or less, furtherpreferably 20 μm or more and 90 μm or less, and particularly preferably25 μm or more and 80 μm or less. When the thickness of the glasssubstrate is in the above range, excellent flexibility may be obtained,and at the same time, sufficient hardness may be obtained. It is alsopossible to suppress curling of the stacked body for a flexible displaydevice. Furthermore, it is preferable in terms of reducing the weight ofthe stacked body for a flexible display device.

4. Functional Layer

The stacked body for a flexible display device in the present disclosuremay include a functional layer on the antistatic layer surface side ofthe substrate layer. Examples of the functional layer may include a hardcoating layer, antireflection layer, an antiglare layer, a scatteringprevention layer, an antifouling layer, and a primer layer.

Also, the functional layer may be a single layer, and may include aplurality of layers. Also, the functional layer may be a layer having asingle function, and may include a plurality of layers having functionsdifferent from each other.

The arrangement of the functional layer is not particularly limited aslong as the functional layer is placed on the antistatic layer surfaceside of the substrate layer. The functional layer may be placed, forexample, between the substrate layer and the antistatic layer, and maybe placed on the antistatic layer, on an opposite surface side to thesubstrate layer.

A hard coating layer is hereinafter exemplified as the functional layer.

(1) Hard Coating Layer

The stacked body for a flexible display device in the present disclosuremay include a hard coating layer on the antistatic layer surface side ofthe substrate layer. The hard coating layer is a member to enhance thesurface hardness. By placing the hard coating layer, scratch resistancemay be improved. Particularly, when the substrate layer is a resinsubstrate, the scratch resistance may be effectively improved by placingthe hard coating layer. Also, when the hard coating layer is included,the contact angle with respect to water after the steel wool testdescribed above, of the antistatic layer side surface of the stackedbody for a flexible display device, may be satisfied.

The arrangement of the hard coating layer is not particularly limited aslong as the hard coating layer is placed on the antistatic layer surfaceside of the substrate layer. For example, the hard coating layer may beplaced, between the substrate layer and the antistatic layer althoughnot shown in the figures, and as shown in FIG. 4 , hard coating layer 4may be placed on the antistatic layer 3, on an opposite surface side tothe substrate layer 2.

As a material of the hard coating layer, for example, an organicmaterial, an inorganic material, and an organic-inorganic compositematerial may be used.

Among the above, the material of the hard coating layer is preferably anorganic material. Specifically, the hard coating layer preferablyinclude a cured product of a resin composition including a polymerizablecompound. The cured product of a resin composition including apolymerizable compound may be obtained by carrying out a polymerizationreaction of a polymerizable compound, by a known method using apolymerization initiator if necessary.

Incidentally, since the polymerizable compound may be similar to thosedescribed in the section of the antistatic layer above, the explanationis omitted herein.

The hard coating layer may include a polymerization initiator ifnecessary. Incidentally, since the polymerization initiator may besimilar to those described in the section of the antistatic layer above,the explanation is omitted herein.

The hard coating layer may further include an additive if necessary. Theadditive is appropriately selected according to the function imparted tothe hard coating layer, and is not particularly limited. Examplesthereof may include an inorganic particle, an organic particle, anultraviolet absorber, an infrared absorber, an antifoulant, an antiglareagent, an antistatic agent, a leveling agent, a surfactant, an easylubricant, various sensitizers, a flame retardant, an adhesive impartingagent, a polymerization inhibitor, an antioxidant, a light stabilizer,and a surface modifier.

The thickness of the hard coating layer may be appropriately selectedaccording to the function of the hard coating layer and the useapplication of the stacked body for a flexible display device. Thethickness of the hard coating layer is preferably, for example, 0.5 μmor more and 50 μm or less, more preferably 1.0 μm or more and 40 μm orless, further preferably 1.5 μm or more and 30 μm or less, andparticularly preferably 2 μm or more and 20 μm or less. When thethickness of hard coating layer is in the above range, sufficienthardness as the hard coating layer may be obtained.

Examples of a method for forming a hard coating layer may include amethod wherein the substrate layer or the antistatic layer is coatedwith a composition for a hard coating layer including the polymerizablecompound, and cured.

5. Impact Absorbing Layer

The stacked body for a flexible display device in the present disclosuremay include an impact absorbing layer on the substrate layer, on anopposite surface side to the antistatic layer, or between the substratelayer and the antistatic layer. By placing the impact absorbing layer,when an impact is imparted to the stacked body for a flexible displaydevice, the impact is absorbed so that the impact resistance may beimproved. Also, when the substrate layer is a glass substrate, the crackof the glass substrate may be suppressed.

The material of the impact absorbing layer is not particularly limitedas long as it is capable of obtaining an impact absorbing layer havingan impact absorbing property, and transparency, and examples thereof mayinclude polyethylene terephthalate (PET), polyethylene naphthalate(PEN), urethane resin, epoxy resin, polyimide, polyamideimide, acrylicresin, triacetyl cellulose (TAC), and silicone resin. One kind of thesematerials may be used alone, and two kinds or more may be used incombination.

The impact absorbing layer may further include an additive if necessary.Examples of the additive may include an inorganic particle, an organicparticle, an ultraviolet absorber, an antioxidant, a light stabilizer, asurfactant, and an adhesive improving agent.

The thickness of the impact absorbing layer may be the thickness capableof absorbing an impact, and is preferably, for example, μm or more and150 μm or less, more preferably 10 μm or more and 120 μm or less, andfurther preferably 15 μm or more and 100 μm or less.

As the impact absorbing layer, for example, a resin film may be used.Also, for example, the impact absorbing layer may be formed by coatingthe substrate layer with a composition for an impact absorbing layer.

6. Adhesive Layer for Adhesion

For example, as shown in FIG. 5 , the stacked body for a flexibledisplay device in the present disclosure may include adhesive layer foradhesion 6 on the substrate layer 2, on an opposite surface side to theantistatic layer 3. The stacked body for a flexible display device maybe adhered to, for example, a display panel via the adhesive layer foradhesion.

The adhesive used for the adhesive layer for adhesion is notparticularly limited as long as it is an adhesive having transparency,and is capable of adhering the stacked body for a flexible displaydevice to, for example, a display panel. Examples thereof may include athermosetting adhesive, an ultraviolet curable adhesive, a two-componentcurable adhesive, a thermal fusion adhesive, and a pressure-sensitiveadhesive (so-called tackiness agent).

Examples of the pressure-sensitive adhesive used for thepressure-sensitive adhesive layer may include an acrylic basedpressure-sensitive adhesive, a silicone based pressure-sensitiveadhesive, a rubber based pressure-sensitive adhesive, and a urethanebased pressure-sensitive adhesive, and may be appropriately selectedaccording to the material of the impact absorbing layer. Among theabove, an acrylic based pressure-sensitive adhesive is preferablebecause of excellent transparency, weather resistance, durability, andheat resistance, and low cost.

The thickness of the adhesive layer for adhesion is preferably, forexample, 10 μm or more and 100 μm or less, more preferably 25 μm or moreand 80 μm or less, and further preferably 40 μm or more and 60 μm orless. When the thickness of the adhesive layer for adhesion is too thin,the stacked body for a flexible display device and the display panel maynot be adhered sufficiently. Also, when the adhesive layer for adhesionis a pressure-sensitive adhesive layer, if the thickness of the adhesivelayer for adhesion is too thin, the effect of making the impactabsorbing layer to be easily deformed, when an impact is imparted to thestacked body for a flexible display device, may not be obtainedsufficiently. Meanwhile, when the thickness of the adhesive layer foradhesion is too thick, the flexibility may be deteriorated.

As the adhesive layer for adhesion, for example, an adhesive film may beused. Also, for example, the adhesive layer for adhesion may be formedby coating a supporting body or the substrate layer, for example, withan adhesive composition.

7. Interlayer Adhesive Layer

In the stacked body for a flexible display device in the presentdisclosure, an interlayer adhesive layer may be placed between eachlayer.

The adhesive used for the interlayer adhesive layer may be similar tothe adhesive used for the adhesive layer for adhesion.

Among the above, as described above, when the impact absorbing layer isplaced on the substrate layer, on the opposite surface side to theantistatic layer; the adhesive layer for adhesion is placed on theimpact absorbing layer, on the opposite surface side to the substratelayer; and the interlayer adhesive layer is placed between the substratelayer and the impact absorbing layer, the adhesive layer for adhesionand the interlayer adhesive layer preferably include thepressure-sensitive adhesive, that is, they are preferablypressure-sensitive adhesive layers.

The pressure-sensitive adhesive layer may be similar to thepressure-sensitive adhesive layer used for the adhesive layer foradhesion.

The thickness of the interlayer adhesive layer, and the forming method,for example, may be similar to the thickness, and the forming method,for example, of the adhesive layer for adhesion.

8. Use Application of Stacked Body for Flexible Display Device

The stacked body for a flexible display device in the present disclosuremay be used as a front panel placed on the observer side than thedisplay panel in a flexible display device. Specifically, the stackedbody for a flexible display device in the present disclosure may be usedas a front panel in a flexible display device such as a foldabledisplay, a rollable display, and a bendable display. Among them, sincethe abrasion resistance at bent portion may be improved, the stackedbody for a flexible display device in the present disclosure may bepreferably used as a front panel in a foldable display.

Also, the stacked body for a flexible display device in the presentdisclosure may be used as a front panel in a display device such assmart phones, tablet terminals, wearable terminals, personal computers,televisions, digital signages, public information displays (PIDs), andcar mounted displays.

B. Stacked Body for Display Device

The stacked body for a display device in the present disclosurecomprises a substrate layer, and an antistatic layer, wherein a contactangle with respect to water, of an antistatic layer side surface of thestacked body for a display device, is 100° or more; a ratio of a contactangle with respect to water after a steel wool test, with respect to aninitial contact angle with respect to water, of the antistatic layerside surface of the stacked body for a display device, is 0.6 or more,wherein, in the steel wool test, the antistatic layer side surface ofthe stacked body for a display device is rubbed with a #0000 steel wool,for 2500 strokes, applying a load of 9.8 N; a surface resistance of theantistatic layer side surface of the stacked body for a display deviceis 9×10¹³Ω/□ or less; and a surface resistance of the antistatic layerside surface of the stacked body for a display device after an erasertest is 9×10¹³Ω/□ or less, wherein, in the eraser test, the antistaticlayer side surface of the stacked body for a display device is rubbedwith a 6 mm diameter eraser, for 2500 strokes, applying a load of 9.8 N.

Since the details of the stacked body for a display device in thepresent disclosure may be similar to the stacked body for a flexibledisplay device described above, the explanation is omitted herein.

C. Flexible Display Device

The flexible display device in the present disclosure comprises: adisplay panel, and the stacked body for a flexible display devicedescribed above placed on an observer side of the display panel.

FIG. 6 is a schematic cross-sectional view illustrating an example of aflexible display device in the present disclosure. As shown in FIG. 6 ,flexible display device 20 comprises display panel 21, and the stackedbody for a flexible display device 1 placed on an observer side of thedisplay panel 21. In the flexible display device 20, the stacked bodyfor a flexible display device 1 and the display panel 21 may be adheredvia, for example, the adhesive layer for adhesion 6 of the stacked bodyfor a flexible display device 1.

When the stacked body for a flexible display device in the presentdisclosure is placed on the surface of the flexible display device, itis placed so that the antistatic layer is on the outer side, and thesubstrate layer is on the inner side.

The method for placing the stacked body for a flexible display device inthe present disclosure on the surface of the flexible display device isnot particularly limited, and examples thereof may include a method viaan adhesive layer.

Examples of the display panel in the present disclosure may include adisplay panel used for a flexible display device such as an organic ELdisplay device, and a liquid crystal display device.

The flexible display device in the present disclosure may include atouch-sensitive panel member between the display panel and the stackedbody for a flexible display device.

The flexible EL display device in the present disclosure is preferablyfoldable. That is, the flexible display device in the present disclosureis preferably a foldable display. The flexible display device in thepresent disclosure is excellent in the abrasion resistance at a bentportion, and is preferable as a foldable display.

Incidentally, the present disclosure is not limited to the embodiments.The embodiments are exemplification, and any other variations areintended to be included in the technical scope of the present disclosureif they have substantially the same constitution as the technical ideadescribed in the claim of the present disclosure and offer similaroperation and effect thereto.

EXAMPLES

The present disclosure is hereinafter explained in further details withreference to Examples and Comparative Examples.

Example 1

Firstly, composition for an antistatic layer 1 was obtained bycompounding each component so as to be the composition shown below.

(Composition of Composition for Antistatic Layer 1)

-   -   Urethane acrylate (product name “UV-7650B” from Mitsubishi        Chemical Corporation): 100 parts by mass (solid content 100%        conversion value)    -   Polymerization initiator (1-hydroxycyclohexylphenyl ketone,        product name “Omnirad184”, from IGM Resins B. V.): 4 parts by        mass    -   Antifoulant (product name “BYK-UV3500” from BYK-Chemie Japan        Co., Ltd.): 0.5 parts by mass (solid content 100% conversion        value)    -   Antistatic agent (PEDOT containing photocuring type resin        composition, product name “Beamset MT-2” from Arakawa Chemical        Industries, Ltd.): 5 parts by mass (solid content 100%        conversion value)    -   Methyl isobutyl ketone: 250 parts by mass

Then, as a substrate layer, a polyimide based resin substrate (productname “Neopulim” from Mitsubishi Gas Chemical Company, Inc.) having athickness of 50 μm was prepared, and a coating film was formed byapplying the composition for an antistatic layer 1 with a bar coater.Thereafter, the coating film was heated at 70° C. for 1 minute toevaporate the solvent in the coating film, and the coating film wascured by irradiating ultraviolet rays with an ultraviolet rayirradiation device (light source H bulb from Fusion UV Systems JapanK.K) under the condition of an oxygen concentration of 200 ppm or lessso that the integrated light amount was 380 mJ/cm² to form an antistaticlayer with a thickness of 10 μm. Thus, a stacked body including asubstrate layer and an antistatic layer was obtained.

Example 2

A stacked body was produced in the same manner as in Example 1 exceptthat the following composition for an antistatic layer 2 was used.

(Composition of Composition for Antistatic Layer 2)

-   -   Polymerization initiator (1-hydroxycyclohexylphenyl ketone,        product name “Omnirad184”, from IGM Resins B. V.): 4 parts by        mass    -   Antifoulant (product name “BYK-UV3500” from BYK-Chemie Japan        Co., Ltd.): 0.5 parts by mass (solid content 100% conversion        value)    -   Antistatic agent (Li salt containing photocuring type resin        composition, product name “Beamset 1604” from Arakawa Chemical        Industries, Ltd.): 100 parts by mass (solid content 100%        conversion value)    -   Methyl isobutyl ketone: 240 parts by mass

Example 3

A stacked body was produced in the same manner as in Example 1 exceptthat the following composition for an antistatic layer 3 was used.

(Composition of Composition for Antistatic Layer 3)

-   -   Urethane acrylate (product name “UV-7650B” from Mitsubishi        Chemical Corporation): 100 parts by mass (solid content 100%        conversion value)    -   Polymerization initiator (1-hydroxycyclohexylphenyl ketone,        product name “Omnirad184”, from IGM Resins B. V.): 4 parts by        mass    -   Antifoulant (product name “BYK-UV3500” from BYK-Chemie Japan        Co., Ltd.): 0.5 parts by mass (solid content 100% conversion        value)    -   Antistatic agent (quaternary ammonium salt containing polymer        type antistatic agent, product name “1SX-1090” from Taisei Fine        Chemical Co., Ltd.): 20 parts by mass (solid content 100%        conversion value)    -   Methyl isobutyl ketone: 290 parts by mass

Example 4

A stacked body was produced in the same manner as in Example 1 exceptthat the following composition for an antistatic layer 4 was used.

(Composition of Composition for Antistatic Layer 4)

-   -   Urethane acrylate (product name “UV-7650B” from Mitsubishi        Chemical Corporation): 100 parts by mass (solid content 100%        conversion value)    -   Polymerization initiator (1-hydroxycyclohexylphenyl ketone,        product name “Omnirad184”, from IGM Resins B. V.): 4 parts by        mass    -   Antifoulant (product name “BYK-UV3500” from BYK-Chemie Japan        Co., Ltd.): 0.5 parts by mass (solid content 100% conversion        value)    -   Antistatic agent (PEDOT containing photocuring type resin        composition, product name “Beamset MT-2” from Arakawa Chemical        Industries, Ltd.): 4 parts by mass (solid content 100%        conversion value)    -   Methyl isobutyl ketone: 250 parts by mass

Example 5

A stacked body was produced in the same manner as in Example 1 exceptthat the following composition for an antistatic layer 5 was used.

(Composition of Composition for Antistatic Layer 5)

-   -   Polymerization initiator (1-hydroxycyclohexylphenyl ketone,        product name “Omnirad184”, from IGM Resins B. V.): 4 parts by        mass    -   Antifoulant (product name “BYK-UV3500” from BYK-Chemie Japan        Co., Ltd.): 0.5 parts by mass (solid content 100% conversion        value)    -   Antistatic agent (Li salt containing photocuring type resin        composition, product name “Beamset 1604” from Arakawa Chemical        Industries, Ltd.): 75 parts by mass (solid content 100%        conversion value)    -   Methyl isobutyl ketone: 240 parts by mass

Example 6

A stacked body was produced in the same manner as in Example 1 exceptthat the following composition for an antistatic layer 6 was used.

(Composition of Composition for Antistatic Layer 6)

-   -   Urethane acrylate (product name “UV-7650B” from Mitsubishi        Chemical Corporation): 100 parts by mass (solid content 100%        conversion value)    -   Polymerization initiator (1-hydroxycyclohexylphenyl ketone,        product name “Omnirad184”, from IGM Resins B. V.): 4 parts by        mass    -   Antifoulant (product name “BYK-UV3500” from BYK-Chemie Japan        Co., Ltd.): 0.5 parts by mass (solid content 100% conversion        value)    -   Antistatic agent (quaternary ammonium salt containing polymer        type antistatic agent, product name “1SX-1090” from Taisei Fine        Chemical Co., Ltd.): 10 parts by mass (solid content 100%        conversion value)    -   Methyl isobutyl ketone: 290 parts by mass

Example 7

A stacked body was produced in the same manner as in Example 1 exceptthat the following composition for an antistatic layer 7 was used.

(Composition of Composition for Antistatic Layer 7)

-   -   Urethane acrylate (product name “UV-7650B” from Mitsubishi        Chemical Corporation): 100 parts by mass (solid content 100%        conversion value)    -   Polymerization initiator (1-hydroxycyclohexylphenyl ketone,        product name “Omnirad184”, from IGM Resins B. V.): 4 parts by        mass    -   Antifoulant (product name “BYK-UV3500” from BYK-Chemie Japan        Co., Ltd.): 0.5 parts by mass (solid content 100% conversion        value)    -   Antistatic agent (quaternary ammonium salt containing polymer        type antistatic agent, product name “1SX-1090” from Taisei Fine        Chemical Co., Ltd.): 25 parts by mass (solid content 100%        conversion value)    -   Methyl isobutyl ketone: 290 parts by mass

Example 8

A stacked body was produced in the same manner as in Example 1 exceptthat the following composition for an antistatic layer 8 was used.

(Composition of Composition for Antistatic Layer 8)

-   -   Urethane acrylate (product name “UV-7650B” from Mitsubishi        Chemical Corporation): 100 parts by mass (solid content 100%        conversion value)    -   Polymerization initiator (1-hydroxycyclohexylphenyl ketone,        product name “Omnirad184”, from IGM Resins B. V.): 4 parts by        mass    -   Antifoulant (product name “BYK-UV3500” from BYK-Chemie Japan        Co., Ltd.): 0.5 parts by mass (solid content 100% conversion        value)    -   Antistatic agent (ATO particle dispersion liquid, product name        “ELECOM V-3560” from JGC Catalysts and Chemicals Ltd.): 15 parts        by mass (solid content 100% conversion value)    -   Methyl isobutyl ketone: 280 parts by mass

Comparative Example 1

A stacked body was produced in the same manner as in Example 1 exceptthat the following composition for an antistatic layer 9 was used.

(Composition of Composition for Antistatic Layer 9)

-   -   Urethane acrylate (product name “UV-7650B” from Mitsubishi        Chemical Corporation): 100 parts by mass (solid content 100%        conversion value)    -   Polymerization initiator (1-hydroxycyclohexylphenyl ketone,        product name “Omnirad184”, from IGM Resins B. V.): 4 parts by        mass    -   Antifoulant (product name “BYK-UV3500” from BYK-Chemie Japan        Co., Ltd.): 0.5 parts by mass (solid content 100% conversion        value)    -   Antistatic agent (PEDOT containing photocuring type resin        composition, product name “Beamset MT-2” from Arakawa Chemical        Industries, Ltd.): 2.5 parts by mass (solid content 100%        conversion value)    -   Methyl isobutyl ketone: 250 parts by mass

Comparative Example 2

A stacked body was produced in the same manner as in Example 1 exceptthat the following composition for an antistatic layer 10 was used.

(Composition of Composition for Antistatic Layer 10)

-   -   Polymerization initiator (1-hydroxycyclohexylphenyl ketone,        product name “Omnirad184”, from IGM Resins B. V.): 4 parts by        mass    -   Antifoulant (product name “BYK-UV3500” from BYK-Chemie Japan        Co., Ltd.): 0.5 parts by mass (solid content 100% conversion        value)    -   Antistatic agent (Li salt containing photocuring type resin        composition, product name “Beamset 1604” from Arakawa Chemical        Industries, Ltd.): 30 parts by mass (solid content 100%        conversion value)    -   Methyl isobutyl ketone: 240 parts by mass

Comparative Example 3

A stacked body was produced in the same manner as in Example 1 exceptthat the following composition for an antistatic layer 11 was used.

(Composition of Composition for Antistatic Layer 11)

-   -   Urethane acrylate (product name “UV-7650B” from Mitsubishi        Chemical Corporation): 100 parts by mass (solid content 100%        conversion value)    -   Polymerization initiator (1-hydroxycyclohexylphenyl ketone,        product name “Omnirad184”, from IGM Resins B. V.): 4 parts by        mass    -   Antifoulant (product name “BYK-UV3500” from BYK-Chemie Japan        Co., Ltd.): 0.5 parts by mass (solid content 100% conversion        value)    -   Antistatic agent (quaternary ammonium salt containing polymer        type antistatic agent, product name “1SX-1090” from Taisei Fine        Chemical Co., Ltd.): 4 parts by mass (solid content 100%        conversion value)    -   Methyl isobutyl ketone: 290 parts by mass

Comparative Example 4

A stacked body was produced in the same manner as in Example 1 exceptthat the following composition for an antistatic layer 12 was used.

(Composition of Composition for Antistatic Layer 12)

-   -   Urethane acrylate (product name “UV-7650B” from Mitsubishi        Chemical Corporation): 100 parts by mass (solid content 100%        conversion value)    -   Polymerization initiator (1-hydroxycyclohexylphenyl ketone,        product name “Omnirad184”, from IGM Resins B. V.): 4 parts by        mass    -   Antifoulant (product name “BYK-UV3500” from BYK-Chemie Japan        Co., Ltd.): 0.5 parts by mass (solid content 100% conversion        value)    -   Antistatic agent (ATO particle dispersion liquid, product name        “ELECOM V-3560” from JGC Catalysts and Chemicals Ltd.): 10 parts        by mass (solid content 100% conversion value)    -   Methyl isobutyl ketone: 280 parts by mass

Comparative Example 5

A stacked body was produced in the same manner as in Example 1 exceptthat the following composition for an antistatic layer 13 was used.

(Composition of Composition for Antistatic Layer 13)

-   -   Urethane acrylate (product name “UV-7650B” from Mitsubishi        Chemical Corporation): 100 parts by mass (solid content 100%        conversion value)    -   Polymerization initiator (1-hydroxycyclohexylphenyl ketone,        product name “Omnirad184”, from IGM Resins B. V.): 4 parts by        mass    -   Antifoulant (product name “BYK-UV3510” from BYK-Chemie Japan        Co., Ltd.): 0.5 parts by mass (solid content 100% conversion        value)    -   Methyl isobutyl ketone: 240 parts by mass

Comparative Example 6

A stacked body was produced in the same manner as in Example 1 exceptthat the following composition for an antistatic layer 14 was used.

(Composition of Composition for Antistatic Layer 14)

-   -   Urethane acrylate (product name “UV-7650B” from Mitsubishi        Chemical Corporation): 100 parts by mass (solid content 100%        conversion value)    -   Polymerization initiator (1-hydroxycyclohexylphenyl ketone,        product name “Omnirad184”, from IGM Resins B. V.): 4 parts by        mass    -   Antifoulant (product name “BYK-UV3500” from BYK-Chemie Japan        Co., Ltd.): 0.5 parts by mass (solid content 100% conversion        value)    -   Methyl isobutyl ketone: 240 parts by mass

Comparative Example 7

A stacked body was produced in the same manner as in Example 1 exceptthat the following composition for an antistatic layer 15 was used.

(Composition of Composition for Antistatic Layer 15)

-   -   Urethane acrylate (product name “UV-7600B” from Mitsubishi        Chemical Corporation): 100 parts by mass (solid content 100%        conversion value)    -   Polymerization initiator (1-hydroxycyclohexylphenyl ketone,        product name “Omnirad184”, from IGM Resins B. V.): 4 parts by        mass    -   Antifoulant (product name “BYK-UV3500” from BYK-Chemie Japan        Co., Ltd.): 0.5 parts by mass (solid content 100% conversion        value)    -   Methyl isobutyl ketone: 240 parts by mass

[Evaluation]

(1) Contact Angle with Respect to Water Before and after Steel Wool Test

The contact angle (initial value) with respect to water, of theantistatic layer side surface of the stacked body in Examples andComparative Examples was measured. Specifically, according to a sessiledrop method based on JIS R3257: 1999, 2 ml of water was dropped on theantistatic layer side surface of the stacked body, and the contact angleimmediately after the drop was measured at ten points using a microscopetype contact angle meter (DropMaster 300 from Kyowa Interface ScienceCo., Ltd.) at 25° C. The arithmetic average value thereof was regardedas the contact angle (initial value) with respect to water of theantistatic layer side surface of the stacked body.

Also, the following steel wool test was carried out to the antistaticlayer side surface of the stacked body in Examples and ComparativeExamples, and the contact angle with respect to water after the steelwool test, of the antistatic layer side surface of the stacked body, wasmeasured. The method for measuring the contact angle with respect towater was similar to the above.

Firstly, in the steel wool test, a stacked body having a size of 5 cm×10cm was prepared. Using #0000 steel wool (Bonstar #0000 from Nippon SteelWool Co., Ltd.), and under the condition wherein the stacked body wasfixed on a glass plate with cellophane tape (registered trademark) fromNichiban Co., Ltd. so that there is no bend or wrinkle, the steel woolwas installed into a jig of 2 cm×2 cm, the stacked body was rubbed for2500 strokes, while applying a load of 9.8 N, at traveling speed of 140mm/sec and traveling distance of 70 mm.

Also, the ratio of the contact angle with respect to water before andafter the steel wool test, was calculated from the following formulawherein the contact angle (initial value) with respect to water, of theantistatic layer side surface of the stacked body was regarded as “A”;and the contact angle with respect to water, of the antistatic layerside surface of the stacked body after the steel wool test was regardedas “B”.

Ratio of contact angle with respect to water=B/A

(2) Sliding Property Before and After Steel Wool Test

The steel wool test described above was carried out to the antistaticlayer side surface of the stacked body in Examples and ComparativeExamples, and the sliding property of the antistatic layer side surfaceof the stacked body before and after the steel wool test was evaluated.Specifically, the antistatic layer side surface of the stacked body wasrubbed with a fingertip in the order of steel wool test-untestedportion, steel wool tested portion, and steel wool test-untested portionat traveling speed of 10 cm/sec, and the sliding property at the steelwool tested portion at that time was evaluated based on the followingcriteria.

-   -   A: 7 or more out of 10 people did not feel scratchy    -   B: 5 or 6 out of 10 people did not feel scratchy    -   C: 6 or 7 out of 10 people felt scratchy    -   D: 8 or more out of 10 people felt scratchy

(3) Surface Resistance Before and After Eraser Test

The following eraser test was carried out to the antistatic layer sidesurface of the stacked body in Examples and Comparative Examples, andthe surface resistance of the antistatic layer side surface of thestacked body before and after the eraser test was measured.

Firstly, in the eraser test, a stacked body having a size of 15 cm×10 cmwas prepared. Then, the eraser test was carried out to the antistaticlayer side surface of the stacked body. Specifically, using a 6 mmdiameter eraser from Minoan Co., Ltd., the eraser was inserted into ajig provided with a 6 mm diameter hole so that 4 mm of the tip of theeraser was exposed from the jig, the jig with the eraser was installedinto a color fastness rubbing tester (tradename “AB-301” from TesterSangyo Co., Ltd.), and the antistatic layer side surface of the stackedbody was rubbed for 2500 strokes, with the eraser, applying a load of9.8 N, at traveling speed of 80 ram/sec, and traveling distance of 40mm.

Then, for the eraser tested portion and the eraser test-untested portionof the antistatic layer side surface of the stacked body, the surfaceresistance was measured. When measuring the surface resistance, themeasurement was carried out after leaving the stacked body to stand for1 hour under environment of temperature of 23±2° C., and humidity of50±10%. The surface resistance was measured by using a resistivity meter(Hiresta-UX MCP-HT type from Nittoseiki Analytech Co., Ltd.), usingMCP-HTO14 URS probe for the eraser tested portion, using MCP-HTP11 UAprobe for the eraser test-untested portion, and at applied voltage of1000 V. For the eraser tested portion and the eraser test-untestedportion of the antistatic layer side surface of the stacked body, thesurface resistance was measured at ten places for the respectiveportions, and the arithmetic average value of the measurement value ofthe ten places was regarded as the surface resistance.

Also, the ratio of the surface resistance before and after the erasertest was calculated from the following formula wherein the surfaceresistance of the eraser test-untested portion of the antistatic layerside surface of the stacked body was regarded as “C”; and the surfaceresistance of the eraser tested portion was regarded as

Ratio of surface resistance=D/C

(5) Sliding Property Before and After Eraser Test

The eraser test described above was carried out to the antistatic layerside surface of the stacked body in Examples and Comparative Examples,and the sliding property of the antistatic layer side surface of thestacked body before and after the eraser test was evaluated.Specifically, the antistatic layer side surface of the stacked body wasrubbed with a fingertip in the order of the eraser test-untestedportion, the eraser tested portion, and the eraser test-untested portionat traveling speed of 10 cm/sec, and the sliding property at the erasertested portion at that time was evaluated based on the followingcriteria.

-   -   A: 7 or more out of 10 people did not feel scratchy    -   B: 5 or 6 out of 10 people did not feel scratchy    -   C: 6 or 7 out of 10 people felt scratchy    -   D: 8 or more out of 10 people felt scratchy

(6) Friction Force Before and After Eraser Test

The eraser test described above was carried out to the antistatic layerside surface of the stacked body in Examples and Comparative Examples,and the friction force of the antistatic layer side surface of thestacked body before and after the eraser test was measured.Specifically, using a 6 mm diameter eraser from Minoan Co., Ltd., theeraser was inserted into a jig provided with a 6 mm diameter hole sothat 4 mm of the tip of the eraser was exposed from the jig, the jigprovided with the eraser was installed into a continuous loadingscratching intensity tester (tradename “TriboGear Type 18” from ShintoScientific Co., Ltd.), and the antistatic layer side surface of thestacked body was rubbed with the eraser, applying a load of 1.96 N andat traveling speed of 840 ram/min in the order of eraser test-untestedportion, eraser tested portion, and eraser test-untested portion tomeasure the friction force. In doing so, as shown in FIG. 2 , the eraserwas moved vertically to the longitudinal direction of the rectangleeraser tested portion 32 as shown with an arrow. And for the frictionforce with respect to the eraser of the eraser tested portion, themaximum value of the friction force was determined. Also, for thefriction force with respect to the eraser in the eraser test-untestedportion, as shown in FIG. 2 , when the point at which the friction forcewith respect to the eraser was the maximum in the eraser tested portion32 was regarded as 0 mm, the average value of the friction force in theeraser test-untested portion 31, in a range of 4.2 mm to 9.8 mm on thebasis of the point (0 mm) described above, was determined.

Also, the ratio of the friction force before and after the eraser testwas calculated from the following formula wherein the average value offriction force of the eraser test-untested portion of the antistaticlayer side surface of the stacked body was regarded as “E”; and themaximum value of the friction force of the eraser tested portion wasregarded as “F”.

Ratio of friction force=F/E

TABLE 1 Avg. of Max of friction friction Antistatic agent Surfaceresistance (Ω/□) force (N) force (N) Added Preeraser Posteraser RatioPreeraser Posteraser amount test (eraser test (eraser of test (erasertest (eraser (pt. test untested tested surface test untested tested Typemass) portion) portion) resistance portion) portion) Example 1 PEDOTcont. photocuring 5 2.9 × 10¹² 4.1 × 10¹² 1.4 3.69 4.81 resincomposition Example 2 Li salt cont. photocuring 100 6.3 × 10¹² 8.0 ×10¹² 1.3 4.37 6.41 resin composition Example 3 Quaternary ammonium salt15 8.0 × 10¹⁰ 1.1 × 10¹¹ 1.4 3.24 4.64 cont. polymer antistatic agentExample 4 PEDOT cont. photocuring 4 3.7 × 10¹² 1.7 × 10¹³ 4.6 4.04 5.93resin composition Example 5 Li salt cont. photocuring 75 6.6 × 10¹² 6.0× 10¹³ 9.1 4.66 6.85 resin composition Example 6 Quaternary ammoniumsalt 10 2.4 × 10¹² 4.4 × 10¹³ 18.3 3.85 5.69 cont. polymer antistaticagent Example 7 Quaternary ammonium salt 25 5.4 × 10⁹ 5.9 × 10⁹ 1.1 2.633.19 cont. polymer antistatic agent Example 8 ATO 4 1.3 × 10¹² 2.9 ×10¹³ 22.3 4.19 6.28 Comp. Ex. 1 PEDOT cont. photocuring 2.5 1.5 × 10¹³>10¹⁴ — 4.91 8.24 resin composition Comp. Ex. 2 Li salt cont.photocuring 30 3.1 × 10¹³ >10¹⁴ — 4.93 7.93 resin composition Comp. Ex.3 Quaternary ammonium salt 4 1.9 × 10¹³ >10¹⁴ — 4.94 8.64 cont. polymerantistatic agent Comp. Ex. 4 ATO 10 8.3 × 10¹³ >10¹⁴ — 4.99 8.83 Comp.Ex. 5 None 0 >10¹⁴ >10¹⁴ — 5.06 9.12 Comp. Ex. 6 None 0 >10¹⁴ >10¹⁴ —5.20 9.49 Comp. Ex. 7 None 0 >10¹⁴ >10¹⁴ — 5.38 9.89 Contact angle withRatio Eraser respect to water (°) of test After Ratio of SW testfriction sliding SW contact sliding force property Initial test angleproperty Example 1 1.30 A 112 108 0.96 A Example 2 1.47 A 109 107 0.98 AExample 3 1.43 A 112 109 0.97 A Example 4 1.47 A 111 107 0.96 A Example5 1.47 A 112 106 0.95 A Example 6 1.48 A 111 102 0.92 A Example 7 1.21 A114 100 0.88 B Example 8 1.50 B 108 106 0.98 A Comp. Ex. 1 1.68 D 112108 0.96 A Comp. Ex. 2 1.61 C 112 104 0.93 A Comp. Ex. 3 1.75 D 111 1010.91 A Comp. Ex. 4 1.77 D 107 72 0.67 C Comp. Ex. 5 1.80 D 108 105 0.97A Comp. Ex. 6 1.82 D 112 108 0.96 A Comp. Ex. 7 1.84 D 112 59 0.53 D

As shown in Table 1, for the samples wherein both of the surfaceresistances before the eraser test and after the eraser test were9×10¹³Ω/□ or less (Examples 1 to 8), all of them were excellent in theeraser test sliding property. However, the samples wherein either one ofthe surface resistances before the eraser test and after the eraser testwas more than 9×10¹³Ω/□ (Comparative Examples 1 to 7), were inferior inthe eraser test sliding property evaluation.

Also, the result of the eraser test sliding property for the samplewherein the ratio of the surface resistance after the eraser test, withrespect to the surface resistance before the eraser test (initialsurface resistance) was more than 20.0 (Example 8), was slightlyinferior than the samples with the ratio of 20.0 or less.

REFERENCE SIGNS LIST

-   -   1: stacked body for a flexible display device    -   2: substrate layer    -   3: antistatic layer    -   4: hard coating layer    -   5: impact absorbing layer    -   6: adhesive layer for adhesion    -   7: interlayer adhesive layer    -   20: flexible display device    -   21: display panel

1. A stacked body for a flexible display device comprising a substratelayer, and an antistatic layer, wherein a contact angle with respect towater, of an antistatic layer side surface of the stacked body for aflexible display device, is 100° or more; a ratio of a contact anglewith respect to water after a steel wool test, with respect to aninitial contact angle with respect to water, of the antistatic layerside surface of the stacked body for a flexible display device, is 0.6or more, wherein, in the steel wool test, the antistatic layer sidesurface of the stacked body for a flexible display device is rubbed witha #0000 steel wool, for 2500 strokes, applying a load of 9.8 N; asurface resistance of the antistatic layer side surface of the stackedbody for a flexible display device is 9×10¹³Ω/□ or less; and a surfaceresistance of the antistatic layer side surface of the stacked body fora flexible display device after an eraser test is 9×10¹³Ω/□ or less,wherein, in the eraser test, the antistatic layer side surface of thestacked body for a flexible display device is rubbed with a 6 mmdiameter eraser, for 2500 strokes, applying a load of 9.8 N.
 2. Thestacked body for a flexible display device according to claim 1, whereina ratio of the surface resistance of the antistatic layer side surfaceof the stacked body for a flexible display device after the eraser test,with respect to an initial surface resistance, is 20.0 or less.
 3. Thestacked body for a flexible display device according to claim 1, whereinthe antistatic layer includes an antifoulant.
 4. The stacked body for aflexible display device according to claim 1, wherein an impactabsorbing layer is included on the substrate layer, on an oppositesurface side to the antistatic layer, or between the substrate layer andthe antistatic layer.
 5. The stacked body for a flexible display deviceaccording to claim 1, wherein a pressure-sensitive adhesive layer foradhesion is included on the substrate layer, on an opposite surface sideto the antistatic layer.
 6. A stacked body for a display devicecomprising a substrate layer, and an antistatic layer, wherein a contactangle with respect to water, of an antistatic layer side surface of thestacked body for a display device, is 100° or more; a ratio of a contactangle with respect to water after a steel wool test, with respect to aninitial contact angle with respect to water, of the antistatic layerside surface of the stacked body for a display device is 0.6 or more,wherein, in the steel wool test, the antistatic layer side surface ofthe stacked body for a display device is rubbed with a #0000 steel wool,for 2500 strokes, applying a load of 9.8 N; a surface resistance of theantistatic layer side surface of the stacked body for a display deviceis 9×10¹³Ω/□ or less; and a surface resistance of the antistatic layerside surface of the stacked body for a display device after an erasertest is 9×10¹³Ω/□ or less, wherein, in the eraser test, the antistaticlayer side surface of the stacked body for a display device is rubbedwith a 6 mm diameter eraser, for 2500 strokes, applying a load of 9.8 N.7. A flexible display device comprising: a display panel, and thestacked body for a flexible display device according to claim 1 placedon an observer side of the display panel.